BASELINE: Update Chromium to 77.0.3865.59

Change-Id: I1e89a5f3b009a9519a6705102ad65c92fe736f21
Reviewed-by: Michael Brüning <michael.bruning@qt.io>

77 files changed, 3327 insertions, 2345 deletions

diff --git a/chromium/third_party/blink/renderer/core/script/BUILD.gn b/chromium/third_party/blink/renderer/core/script/BUILD.gn
index 1346b025962..ac7886ede65 100644
--- a/chromium/third_party/blink/renderer/core/script/BUILD.gn
+++ b/chromium/third_party/blink/renderer/core/script/BUILD.gn
@@ -58,6 +58,8 @@ blink_core_sources("script") {
     "script_runner.cc",
     "script_runner.h",
     "script_scheduling_type.h",
+    "value_wrapper_synthetic_module_script.cc",
+    "value_wrapper_synthetic_module_script.h",
     "worker_modulator_impl.cc",
     "worker_modulator_impl.h",
     "worklet_modulator_impl.cc",
@@ -73,3 +75,24 @@ blink_core_sources("script") {
 
   jumbo_excluded_sources = [ "modulator.cc" ]  # https://crbug.com/716395
 }
+
+copy("layered_apis_elements_virtual_scroller_js") {
+  testonly = true
+
+  sources = [
+    "resources/layered_api/elements/virtual-scroller/find-element.mjs",
+    "resources/layered_api/elements/virtual-scroller/sets.mjs",
+    "resources/layered_api/elements/virtual-scroller/visibility-manager.mjs",
+  ]
+
+  outputs = [
+    "{{source_gen_dir}}/{{source_file_part}}",
+  ]
+}
+
+group("js_files_for_web_tests") {
+  testonly = true
+  data_deps = [
+    ":layered_apis_elements_virtual_scroller_js",
+  ]
+}
diff --git a/chromium/third_party/blink/renderer/core/script/classic_pending_script.cc b/chromium/third_party/blink/renderer/core/script/classic_pending_script.cc
index 3bd0f996731..67703f93bfd 100644
--- a/chromium/third_party/blink/renderer/core/script/classic_pending_script.cc
+++ b/chromium/third_party/blink/renderer/core/script/classic_pending_script.cc
@@ -18,10 +18,11 @@
 #include "third_party/blink/renderer/core/script/document_write_intervention.h"
 #include "third_party/blink/renderer/core/script/script_loader.h"
 #include "third_party/blink/renderer/platform/bindings/script_state.h"
-#include "third_party/blink/renderer/platform/histogram.h"
+#include "third_party/blink/renderer/platform/instrumentation/histogram.h"
 #include "third_party/blink/renderer/platform/instrumentation/tracing/trace_event.h"
 #include "third_party/blink/renderer/platform/loader/allowed_by_nosniff.h"
 #include "third_party/blink/renderer/platform/loader/fetch/cached_metadata.h"
+#include "third_party/blink/renderer/platform/loader/fetch/detachable_use_counter.h"
 #include "third_party/blink/renderer/platform/loader/fetch/memory_cache.h"
 #include "third_party/blink/renderer/platform/loader/fetch/raw_resource.h"
 #include "third_party/blink/renderer/platform/loader/fetch/resource_client.h"
@@ -249,10 +250,13 @@ void ClassicPendingScript::NotifyFinished(Resource* resource) {
 
     // It is possible to get back a script resource with integrity metadata
     // for a request with an empty integrity attribute. In that case, the
-    // integrity check should be skipped, so this check ensures that the
-    // integrity attribute isn't empty in addition to checking if the
-    // resource has empty integrity metadata.
-    if (!element->IntegrityAttributeValue().IsEmpty()) {
+    // integrity check should be skipped, as the integrity may not have been
+    // "meant" for this specific request. If the resource is being served from
+    // the preload cache however, we know any associated integrity metadata and
+    // checks were destined for this request, so we cannot skip the integrity
+    // check.
+    if (!element->IntegrityAttributeValue().IsEmpty() ||
+        GetResource()->IsLinkPreload()) {
       integrity_failure_ = GetResource()->IntegrityDisposition() !=
                            ResourceIntegrityDisposition::kPassed;
     }
@@ -276,7 +280,7 @@ void ClassicPendingScript::NotifyFinished(Resource* resource) {
   AdvanceReadyState(error_occurred ? kErrorOccurred : kReady);
 }
 
-void ClassicPendingScript::Trace(blink::Visitor* visitor) {
+void ClassicPendingScript::Trace(Visitor* visitor) {
   ResourceClient::Trace(visitor);
   MemoryPressureListener::Trace(visitor);
   PendingScript::Trace(visitor);
@@ -342,7 +346,7 @@ ClassicScript* ClassicPendingScript::GetSource(const KURL& document_url) const {
   auto* fetcher = GetElement()->GetDocument().ContextDocument()->Fetcher();
   // If the MIME check fails, which is considered as load failure.
   if (!AllowedByNosniff::MimeTypeAsScript(
-          fetcher->Context(), &fetcher->GetConsoleLogger(),
+          fetcher->GetUseCounter(), &fetcher->GetConsoleLogger(),
           resource->GetResponse(), AllowedByNosniff::MimeTypeCheck::kLax)) {
     return nullptr;
   }
diff --git a/chromium/third_party/blink/renderer/core/script/classic_pending_script.h b/chromium/third_party/blink/renderer/core/script/classic_pending_script.h
index c9e135de659..ca495ebdd16 100644
--- a/chromium/third_party/blink/renderer/core/script/classic_pending_script.h
+++ b/chromium/third_party/blink/renderer/core/script/classic_pending_script.h
@@ -10,8 +10,8 @@
 #include "third_party/blink/renderer/core/loader/resource/script_resource.h"
 #include "third_party/blink/renderer/core/script/classic_script.h"
 #include "third_party/blink/renderer/core/script/pending_script.h"
+#include "third_party/blink/renderer/platform/instrumentation/memory_pressure_listener.h"
 #include "third_party/blink/renderer/platform/loader/fetch/fetch_parameters.h"
-#include "third_party/blink/renderer/platform/memory_pressure_listener.h"
 
 namespace blink {
 
@@ -58,7 +58,7 @@ class CORE_EXPORT ClassicPendingScript final : public PendingScript,
   void SetStreamer(ScriptStreamer*);
   void StreamingFinished();
 
-  void Trace(blink::Visitor*) override;
+  void Trace(Visitor*) override;
 
   mojom::ScriptType GetScriptType() const override {
     return mojom::ScriptType::kClassic;
diff --git a/chromium/third_party/blink/renderer/core/script/classic_script.cc b/chromium/third_party/blink/renderer/core/script/classic_script.cc
index afe840f1bb7..df884115ba2 100644
--- a/chromium/third_party/blink/renderer/core/script/classic_script.cc
+++ b/chromium/third_party/blink/renderer/core/script/classic_script.cc
@@ -13,7 +13,7 @@
 
 namespace blink {
 
-void ClassicScript::Trace(blink::Visitor* visitor) {
+void ClassicScript::Trace(Visitor* visitor) {
   Script::Trace(visitor);
   visitor->Trace(script_source_code_);
 }
diff --git a/chromium/third_party/blink/renderer/core/script/classic_script.h b/chromium/third_party/blink/renderer/core/script/classic_script.h
index b5da0ea28d7..e64a2118b1e 100644
--- a/chromium/third_party/blink/renderer/core/script/classic_script.h
+++ b/chromium/third_party/blink/renderer/core/script/classic_script.h
@@ -24,7 +24,7 @@ class CORE_EXPORT ClassicScript final : public Script {
         script_source_code_(script_source_code),
         sanitize_script_errors_(sanitize_script_errors) {}
 
-  void Trace(blink::Visitor*) override;
+  void Trace(Visitor*) override;
 
   const ScriptSourceCode& GetScriptSourceCode() const {
     return script_source_code_;
diff --git a/chromium/third_party/blink/renderer/core/script/document_write_intervention.cc b/chromium/third_party/blink/renderer/core/script/document_write_intervention.cc
index fbe4bfc38f9..e4bb75221db 100644
--- a/chromium/third_party/blink/renderer/core/script/document_write_intervention.cc
+++ b/chromium/third_party/blink/renderer/core/script/document_write_intervention.cc
@@ -4,7 +4,7 @@
 
 #include "third_party/blink/renderer/core/script/document_write_intervention.h"
 
-#include "third_party/blink/public/mojom/fetch/fetch_api_request.mojom-shared.h"
+#include "third_party/blink/public/mojom/fetch/fetch_api_request.mojom-blink.h"
 #include "third_party/blink/public/platform/web_effective_connection_type.h"
 #include "third_party/blink/renderer/core/frame/local_frame.h"
 #include "third_party/blink/renderer/core/frame/local_frame_client.h"
@@ -34,7 +34,7 @@ void EmitWarningMayBeBlocked(const String& url, Document& document) {
   document.AddConsoleMessage(
       ConsoleMessage::Create(mojom::ConsoleMessageSource::kJavaScript,
                              mojom::ConsoleMessageLevel::kWarning, message));
-  DVLOG(1) << message.Utf8().data();
+  DVLOG(1) << message.Utf8();
 }
 
 void EmitWarningNotBlocked(const String& url, Document& document) {
diff --git a/chromium/third_party/blink/renderer/core/script/dynamic_module_resolver.cc b/chromium/third_party/blink/renderer/core/script/dynamic_module_resolver.cc
index b8249e5a431..63ffbe076b0 100644
--- a/chromium/third_party/blink/renderer/core/script/dynamic_module_resolver.cc
+++ b/chromium/third_party/blink/renderer/core/script/dynamic_module_resolver.cc
@@ -27,7 +27,7 @@ class DynamicImportTreeClient final : public ModuleTreeClient {
                           ScriptPromiseResolver* promise_resolver)
       : url_(url), modulator_(modulator), promise_resolver_(promise_resolver) {}
 
-  void Trace(blink::Visitor*) override;
+  void Trace(Visitor*) override;
 
  private:
   // Implements ModuleTreeClient:
@@ -54,31 +54,30 @@ void DynamicImportTreeClient::NotifyModuleTreeLoadFinished(
   ScriptState::Scope scope(script_state);
   v8::Isolate* isolate = script_state->GetIsolate();
 
-  // <spec step="2.5">If result is null, then:</spec>
+  // <spec step="6">If result is null, then:</spec>
   if (!module_script) {
-    // <spec step="2.5.1">Let completion be Completion { [[Type]]: throw,
+    // <spec step="6.1">Let completion be Completion { [[Type]]: throw,
     // [[Value]]: a new TypeError, [[Target]]: empty }.</spec>
     v8::Local<v8::Value> error = V8ThrowException::CreateTypeError(
         isolate,
         "Failed to fetch dynamically imported module: " + url_.GetString());
 
-    // <spec step="2.5.2">Perform FinishDynamicImport(referencingScriptOrModule,
+    // <spec step="6.2">Perform FinishDynamicImport(referencingScriptOrModule,
     // specifier, promiseCapability, completion).</spec>
     promise_resolver_->Reject(error);
 
-    // <spec step="2.5.3">Return.</spec>
+    // <spec step="6.3">Return.</spec>
     return;
   }
 
-  // <spec step="2.6">Run the module script result, with the rethrow errors
+  // <spec step="7">Run the module script result, with the rethrow errors
   // boolean set to true.</spec>
   ScriptValue error = modulator_->ExecuteModule(
       module_script, Modulator::CaptureEvalErrorFlag::kCapture);
 
-  // <spec step="2.7">If running the module script throws an exception,
-  // ...</spec>
+  // <spec step="8">If running the module script throws an exception, ...</spec>
   if (!error.IsEmpty()) {
-    // <spec step="2.7">... then perform
+    // <spec step="8">... then perform
     // FinishDynamicImport(referencingScriptOrModule, specifier,
     // promiseCapability, the thrown exception completion).</spec>
     //
@@ -93,7 +92,7 @@ void DynamicImportTreeClient::NotifyModuleTreeLoadFinished(
     return;
   }
 
-  // <spec step="2.8">Otherwise, perform
+  // <spec step="9">Otherwise, perform
   // FinishDynamicImport(referencingScriptOrModule, specifier,
   // promiseCapability, NormalCompletion(undefined)).</spec>
   //
@@ -142,7 +141,7 @@ void DynamicImportTreeClient::NotifyModuleTreeLoadFinished(
   promise_resolver_->Resolve(module_namespace);
 }
 
-void DynamicImportTreeClient::Trace(blink::Visitor* visitor) {
+void DynamicImportTreeClient::Trace(Visitor* visitor) {
   visitor->Trace(modulator_);
   visitor->Trace(promise_resolver_);
   ModuleTreeClient::Trace(visitor);
@@ -150,7 +149,7 @@ void DynamicImportTreeClient::Trace(blink::Visitor* visitor) {
 
 }  // namespace
 
-void DynamicModuleResolver::Trace(blink::Visitor* visitor) {
+void DynamicModuleResolver::Trace(Visitor* visitor) {
   visitor->Trace(modulator_);
 }
 
@@ -173,13 +172,10 @@ void DynamicModuleResolver::ResolveDynamically(
   // (in ResolveModuleSpecifier()) and we need to clear the flag before that.
   modulator_->ClearIsAcquiringImportMaps();
 
-  // <spec step="1">Let referencing script be
+  // <spec step="4.1">Let referencing script be
   // referencingScriptOrModule.[[HostDefined]].</spec>
 
-  // <spec step="2">Run the following steps in parallel:</spec>
-
-  // <spec step="2.1">Let url be the result of resolving a module specifier
-  // given referencing script's base URL and specifier.</spec>
+  // <spec step="4.3">Set base URL to referencing script's base URL.</spec>
   KURL base_url = referrer_info.BaseURL();
   if (base_url.IsNull()) {
     // ReferrerScriptInfo::BaseURL returns null if it should defer to referrer
@@ -187,25 +183,39 @@ void DynamicModuleResolver::ResolveDynamically(
     base_url = referrer_resource_url;
   }
   if (base_url.IsNull()) {
-    // In some cases, "referencing script" may not exist. Use the document's
-    // base URL as last resort.
-    // TODO(kouhei): Revisit this after
-    //               https://github.com/whatwg/html/issues/3295 resolved.
+    // The case where "referencing script" doesn't exist.
+    //
+    // <spec step="1">Let settings object be the current settings object.</spec>
+    //
+    // <spec step="2">Let base URL be settings object's API base URL.</spec>
     base_url = ExecutionContext::From(modulator_->GetScriptState())->BaseURL();
   }
   DCHECK(!base_url.IsNull());
 
+  // <spec step="5">Fetch an import() module script graph given specifier, base
+  // URL, settings object, and fetch options. Wait until the algorithm
+  // asynchronously completes with result.</spec>
+  //
+  // <specdef label="fetch-an-import()-module-script-graph"
+  // href="https://html.spec.whatwg.org/C/#fetch-an-import()-module-script-graph">
+
+  // <spec label="fetch-an-import()-module-script-graph" step="1">Let url be the
+  // result of resolving a module specifier given base URL and specifier.</spec>
   KURL url = modulator_->ResolveModuleSpecifier(specifier, base_url);
+
+  // <spec label="fetch-an-import()-module-script-graph" step="2">If url is
+  // failure, then asynchronously complete this algorithm with null, and abort
+  // these steps.</spec>
   if (!url.IsValid()) {
-    // <spec step="2.2">If url is failure, then:</spec>
+    // <spec step="6">If result is null, then:</spec>
     //
-    // <spec step="2.2.1">Let completion be Completion { [[Type]]: throw,
+    // <spec step="6.1">Let completion be Completion { [[Type]]: throw,
     // [[Value]]: a new TypeError, [[Target]]: empty }.</spec>
     v8::Isolate* isolate = modulator_->GetScriptState()->GetIsolate();
     v8::Local<v8::Value> error = V8ThrowException::CreateTypeError(
         isolate, "Failed to resolve module specifier '" + specifier + "'");
 
-    // <spec step="2.2.2">Perform FinishDynamicImport(referencingScriptOrModule,
+    // <spec step="6.2">Perform FinishDynamicImport(referencingScriptOrModule,
     // specifier, promiseCapability, completion).</spec>
     //
     // <spec
@@ -215,18 +225,19 @@ void DynamicModuleResolver::ResolveDynamically(
     // »).</spec>
     promise_resolver->Reject(error);
 
-    // <spec step="2.2.3">Return.</spec>
+    // <spec step="6.3">Return.</spec>
     return;
   }
 
-  // <spec step="2.3">Let options be the descendant script fetch options for
-  // referencing script's fetch options.</spec>
+  // <spec step="4.4">Set fetch options to the descendant script fetch options
+  // for referencing script's fetch options.</spec>
   //
   // <spec
   // href="https://html.spec.whatwg.org/C/#descendant-script-fetch-options"> For
   // any given script fetch options options, the descendant script fetch options
   // are a new script fetch options whose items all have the same values, except
   // for the integrity metadata, which is instead the empty string.</spec>
+  //
   // TODO(domfarolino): It has not yet been decided how a script's "importance"
   // should affect its dynamic imports. There is discussion at
   // https://github.com/whatwg/html/issues/3670, but for now there is no effect,
@@ -239,9 +250,12 @@ void DynamicModuleResolver::ResolveDynamically(
                              referrer_info.GetReferrerPolicy(),
                              mojom::FetchImportanceMode::kImportanceAuto);
 
-  // <spec step="2.4">Fetch a module script graph given url, referencing
-  // script's settings object, "script", and options. Wait until the algorithm
-  // asynchronously completes with result.</spec>
+  // <spec label="fetch-an-import()-module-script-graph" step="3">Fetch a single
+  // module script given url, settings object, "script", options, settings
+  // object, "client", and with the top-level module fetch flag set. If the
+  // caller of this algorithm specified custom perform the fetch steps, pass
+  // those along as well. Wait until the algorithm asynchronously completes with
+  // result.</spec>
   auto* tree_client = MakeGarbageCollected<DynamicImportTreeClient>(
       url, modulator_.Get(), promise_resolver);
   // TODO(kouhei): ExecutionContext::From(modulator_->GetScriptState()) is
@@ -254,10 +268,10 @@ void DynamicModuleResolver::ResolveDynamically(
                         mojom::RequestContextType::SCRIPT, options,
                         ModuleScriptCustomFetchType::kNone, tree_client);
 
-  // Steps 2.[5-8] are implemented at
+  // Steps 6-9 are implemented at
   // DynamicImportTreeClient::NotifyModuleLoadFinished.
 
-  // <spec step="3">Return undefined.</spec>
+  // <spec step="10">Return undefined.</spec>
 }
 
 }  // namespace blink
diff --git a/chromium/third_party/blink/renderer/core/script/dynamic_module_resolver.h b/chromium/third_party/blink/renderer/core/script/dynamic_module_resolver.h
index b97df2d5d5b..e73c78d383b 100644
--- a/chromium/third_party/blink/renderer/core/script/dynamic_module_resolver.h
+++ b/chromium/third_party/blink/renderer/core/script/dynamic_module_resolver.h
@@ -23,7 +23,7 @@ class ScriptPromiseResolver;
 class CORE_EXPORT DynamicModuleResolver final
     : public GarbageCollected<DynamicModuleResolver> {
  public:
-  void Trace(blink::Visitor*);
+  void Trace(Visitor*);
 
   explicit DynamicModuleResolver(Modulator* modulator)
       : modulator_(modulator) {}
diff --git a/chromium/third_party/blink/renderer/core/script/dynamic_module_resolver_test.cc b/chromium/third_party/blink/renderer/core/script/dynamic_module_resolver_test.cc
index 90b5bbb5ef7..c85586c2393 100644
--- a/chromium/third_party/blink/renderer/core/script/dynamic_module_resolver_test.cc
+++ b/chromium/third_party/blink/renderer/core/script/dynamic_module_resolver_test.cc
@@ -47,7 +47,7 @@ class DynamicModuleResolverTestModulator final : public DummyModulator {
   }
   bool fetch_tree_was_called() const { return fetch_tree_was_called_; }
 
-  void Trace(blink::Visitor*) override;
+  void Trace(Visitor*) override;
 
  private:
   // Implements Modulator:
@@ -101,7 +101,7 @@ class DynamicModuleResolverTestModulator final : public DummyModulator {
   bool fetch_tree_was_called_ = false;
 };
 
-void DynamicModuleResolverTestModulator::Trace(blink::Visitor* visitor) {
+void DynamicModuleResolverTestModulator::Trace(Visitor* visitor) {
   visitor->Trace(script_state_);
   visitor->Trace(pending_client_);
   DummyModulator::Trace(visitor);
@@ -110,7 +110,7 @@ void DynamicModuleResolverTestModulator::Trace(blink::Visitor* visitor) {
 // CaptureExportedStringFunction implements a javascript function
 // with a single argument of type module namespace.
 // CaptureExportedStringFunction captures the exported string value
-// from the module namespace as a blink::String, exposed via CapturedValue().
+// from the module namespace as a WTF::String, exposed via CapturedValue().
 class CaptureExportedStringFunction final : public ScriptFunction {
  public:
   CaptureExportedStringFunction(ScriptState* script_state,
diff --git a/chromium/third_party/blink/renderer/core/script/fetch_client_settings_object_impl.h b/chromium/third_party/blink/renderer/core/script/fetch_client_settings_object_impl.h
index 1be2d76fbaf..a01b4a1df40 100644
--- a/chromium/third_party/blink/renderer/core/script/fetch_client_settings_object_impl.h
+++ b/chromium/third_party/blink/renderer/core/script/fetch_client_settings_object_impl.h
@@ -5,14 +5,14 @@
 #ifndef THIRD_PARTY_BLINK_RENDERER_CORE_SCRIPT_FETCH_CLIENT_SETTINGS_OBJECT_IMPL_H_
 #define THIRD_PARTY_BLINK_RENDERER_CORE_SCRIPT_FETCH_CLIENT_SETTINGS_OBJECT_IMPL_H_
 
-#include "services/network/public/mojom/referrer_policy.mojom-shared.h"
+#include "services/network/public/mojom/referrer_policy.mojom-blink.h"
 #include "third_party/blink/renderer/core/core_export.h"
-#include "third_party/blink/renderer/platform/cross_thread_copier.h"
 #include "third_party/blink/renderer/platform/heap/member.h"
 #include "third_party/blink/renderer/platform/loader/fetch/fetch_client_settings_object.h"
 #include "third_party/blink/renderer/platform/loader/fetch/https_state.h"
 #include "third_party/blink/renderer/platform/weborigin/kurl.h"
 #include "third_party/blink/renderer/platform/weborigin/security_origin.h"
+#include "third_party/blink/renderer/platform/wtf/cross_thread_copier.h"
 
 namespace blink {
 
diff --git a/chromium/third_party/blink/renderer/core/script/generate_lapi_grdp.py b/chromium/third_party/blink/renderer/core/script/generate_lapi_grdp.py
index a05172b2019..fcb15ba5047 100755
--- a/chromium/third_party/blink/renderer/core/script/generate_lapi_grdp.py
+++ b/chromium/third_party/blink/renderer/core/script/generate_lapi_grdp.py
@@ -5,6 +5,7 @@
 
 import sys
 import os
+import re
 
 
 def main():
@@ -40,42 +41,42 @@ def main():
     -->'''
 
     resource_list_in_header_file = ''
-    modules = set()
-
+    # A list of (name, path)
+    modules = []
     for root, _, filenames in sorted(os.walk(input_path)):
-        relroot = os.path.relpath(root, input_path)
-        if relroot == '.':
-            # We don't include top-level files under resources/layered_api,
-            # including generated resources.grdp.
-            continue
-
-        # Get e.g. "kKvStorage" for kv-storage.
-        module_name = relroot.split('/')[0]
-        module_name = "k" + module_name.title().replace('-', '')
-        modules.add(module_name)
-
-        for filename in sorted(filenames):
-            if filename.startswith('.') or filename.startswith(
-                    'README') or filename.startswith('OWNERS'):
-                continue
-            relpath = os.path.relpath(os.path.join(root, filename), input_path)
-            relpath = relpath.replace('\\', '/')
-            resource_id = relpath
-            resource_id = resource_id.replace('/', '_')
-            resource_id = resource_id.replace('-', '_')
-            resource_id = resource_id.replace('.', '_')
-            resource_id = resource_id.upper()
-            resource_id = "IDR_LAYERED_API_" + resource_id
-            resource_list_in_header_file += \
-                '    {"%s",\n     %s,\n     Module::%s},\n' % (relpath, resource_id, module_name)
-            print >> output_grdp_file, (
-                '  <include name="%s" file="%s/%s" type="BINDATA" skip_minify="true" compress="gzip"/>'
-                % (resource_id, input_relative_path, relpath))
-        resource_list_in_header_file += '\n'
+        # A directory represents a built-in module if
+        #  - it contains index.mjs (web-exposed module) or
+        #  - the directory name is 'internal' (private module)
+        if 'index.mjs' in filenames or re.search(r'\binternal$', root):
+            # Get e.g. "kKvStorage" for kv-storage.
+            module_name = os.path.relpath(root, input_path)
+            module_name = "k" + re.sub(r'\W', '', module_name.title())
+            modules.append((module_name, root))
+
+    for module_name, module_path in modules:
+        for root, _, filenames in sorted(os.walk(module_path)):
+            for filename in sorted(filenames):
+                if filename.startswith('.') or filename.startswith(
+                        'README') or filename.startswith('OWNERS'):
+                    continue
+                relpath = os.path.relpath(os.path.join(root, filename), input_path)
+                relpath = relpath.replace('\\', '/')
+                resource_id = relpath
+                resource_id = resource_id.replace('/', '_')
+                resource_id = resource_id.replace('-', '_')
+                resource_id = resource_id.replace('.', '_')
+                resource_id = resource_id.upper()
+                resource_id = "IDR_LAYERED_API_" + resource_id
+                resource_list_in_header_file += \
+                    '    {"%s",\n     %s,\n     Module::%s},\n' % (relpath, resource_id, module_name)
+                print >> output_grdp_file, (
+                    '  <include name="%s" file="%s/%s" type="BINDATA" skip_minify="true" compress="gzip"/>'
+                    % (resource_id, input_relative_path, relpath))
+            resource_list_in_header_file += '\n'
     print >> output_grdp_file, '</grit-part>'
 
     module_list_in_header_file = ''
-    for module in modules:
+    for module, _ in modules:
         module_list_in_header_file += ('  %s,\n' % module)
 
     print >> output_module_header_file, '''// Copyright 2019 The Chromium Authors. All rights reserved.
diff --git a/chromium/third_party/blink/renderer/core/script/html_parser_script_runner.cc b/chromium/third_party/blink/renderer/core/script/html_parser_script_runner.cc
index 2a22c04baf2..2bd8365bb0e 100644
--- a/chromium/third_party/blink/renderer/core/script/html_parser_script_runner.cc
+++ b/chromium/third_party/blink/renderer/core/script/html_parser_script_runner.cc
@@ -27,6 +27,7 @@
 
 #include <inttypes.h>
 #include <memory>
+#include "services/metrics/public/cpp/ukm_builders.h"
 #include "third_party/blink/public/platform/platform.h"
 #include "third_party/blink/public/platform/task_type.h"
 #include "third_party/blink/renderer/core/dom/document_parser_timing.h"
@@ -39,7 +40,7 @@
 #include "third_party/blink/renderer/core/script/script_loader.h"
 #include "third_party/blink/renderer/platform/bindings/microtask.h"
 #include "third_party/blink/renderer/platform/bindings/v8_per_isolate_data.h"
-#include "third_party/blink/renderer/platform/histogram.h"
+#include "third_party/blink/renderer/platform/instrumentation/histogram.h"
 #include "third_party/blink/renderer/platform/instrumentation/tracing/trace_event.h"
 #include "third_party/blink/renderer/platform/instrumentation/tracing/traced_value.h"
 
@@ -160,6 +161,11 @@ void HTMLParserScriptRunner::Detach() {
     parser_blocking_script_->Dispose();
   parser_blocking_script_ = nullptr;
 
+  while (!force_deferred_scripts_.IsEmpty()) {
+    PendingScript* pending_script = force_deferred_scripts_.TakeFirst();
+    pending_script->Dispose();
+  }
+
   while (!scripts_to_execute_after_parsing_.IsEmpty()) {
     PendingScript* pending_script =
         scripts_to_execute_after_parsing_.TakeFirst();
@@ -299,7 +305,14 @@ void HTMLParserScriptRunner::PendingScriptFinished(
     return;
   }
 
-  host_->NotifyScriptLoaded(pending_script);
+  // Posting the script execution part to a new task so that we can allow
+  // yielding for cooperative scheduling. Cooperative scheduling requires that
+  // the Blink C++ stack be thin when it executes JavaScript.
+  document_->GetTaskRunner(TaskType::kInternalContinueScriptLoading)
+      ->PostTask(FROM_HERE,
+                 WTF::Bind(&HTMLParserScriptRunnerHost::NotifyScriptLoaded,
+                           WrapPersistent(host_.Get()),
+                           WrapPersistent(pending_script)));
 }
 
 // <specdef href="https://html.spec.whatwg.org/C/#scriptEndTag">
@@ -412,38 +425,61 @@ void HTMLParserScriptRunner::ExecuteScriptsWaitingForResources() {
   ExecuteParsingBlockingScripts();
 }
 
+PendingScript* HTMLParserScriptRunner::TryTakeReadyScriptWaitingForParsing(
+    HeapDeque<Member<PendingScript>>* waiting_scripts) {
+  DCHECK(!waiting_scripts->IsEmpty());
+
+  // <spec step="3.1">Spin the event loop until the first script in the list
+  // of scripts that will execute when the document has finished parsing has
+  // its "ready to be parser-executed" flag set and the parser's Document has
+  // no style sheet that is blocking scripts.</spec>
+  //
+  // TODO(hiroshige): Add check for style sheet blocking defer scripts
+  // https://github.com/whatwg/html/issues/3890
+  if (!waiting_scripts->front()->IsReady()) {
+    waiting_scripts->front()->WatchForLoad(this);
+    TraceParserBlockingScript(waiting_scripts->front().Get(),
+                              !document_->IsScriptExecutionReady());
+    waiting_scripts->front()->MarkParserBlockingLoadStartTime();
+    return nullptr;
+  }
+  return waiting_scripts->TakeFirst();
+}
+
 // <specdef href="https://html.spec.whatwg.org/C/#stop-parsing">
 //
 // <spec step="3">If the list of scripts that will execute when the document has
 // finished parsing is not empty, run these substeps:</spec>
+//
+// This will also run any forced deferred scripts before running any developer
+// deferred scripts.
 bool HTMLParserScriptRunner::ExecuteScriptsWaitingForParsing() {
   TRACE_EVENT0("blink",
                "HTMLParserScriptRunner::executeScriptsWaitingForParsing");
 
-  while (!scripts_to_execute_after_parsing_.IsEmpty()) {
+  while (!force_deferred_scripts_.IsEmpty() ||
+         !scripts_to_execute_after_parsing_.IsEmpty()) {
     DCHECK(!IsExecutingScript());
     DCHECK(!HasParserBlockingScript());
-    DCHECK(scripts_to_execute_after_parsing_.front()->IsExternalOrModule());
-
-    // <spec step="3.1">Spin the event loop until the first script in the list
-    // of scripts that will execute when the document has finished parsing has
-    // its "ready to be parser-executed" flag set and the parser's Document has
-    // no style sheet that is blocking scripts.</spec>
-    //
-    // TODO(hiroshige): Is the latter part checked anywhere?
-    if (!scripts_to_execute_after_parsing_.front()->IsReady()) {
-      scripts_to_execute_after_parsing_.front()->WatchForLoad(this);
-      TraceParserBlockingScript(scripts_to_execute_after_parsing_.front().Get(),
-                                !document_->IsScriptExecutionReady());
-      scripts_to_execute_after_parsing_.front()
-          ->MarkParserBlockingLoadStartTime();
-      return false;
-    }
+    DCHECK(scripts_to_execute_after_parsing_.IsEmpty() ||
+           scripts_to_execute_after_parsing_.front()->IsExternalOrModule());
 
     // <spec step="3.3">Remove the first script element from the list of scripts
     // that will execute when the document has finished parsing (i.e. shift out
     // the first entry in the list).</spec>
-    PendingScript* first = scripts_to_execute_after_parsing_.TakeFirst();
+    PendingScript* first = nullptr;
+
+    // First execute the scripts that were forced-deferred. If no such scripts
+    // are present, then try executing scripts that were deferred by the web
+    // developer.
+    if (!force_deferred_scripts_.IsEmpty()) {
+      first = TryTakeReadyScriptWaitingForParsing(&force_deferred_scripts_);
+    } else {
+      first = TryTakeReadyScriptWaitingForParsing(
+          &scripts_to_execute_after_parsing_);
+    }
+    if (!first)
+      return false;
 
     // <spec step="3.2">Execute the first script in the list of scripts that
     // will execute when the document has finished parsing.</spec>
@@ -494,6 +530,7 @@ void HTMLParserScriptRunner::RequestDeferredScript(
     pending_script->StartStreamingIfPossible();
   }
 
+  DCHECK(!script_loader->IsForceDeferred());
   DCHECK(pending_script->IsExternalOrModule());
 
   // <spec href="https://html.spec.whatwg.org/C/#prepare-a-script"
@@ -503,6 +540,25 @@ void HTMLParserScriptRunner::RequestDeferredScript(
   scripts_to_execute_after_parsing_.push_back(pending_script);
 }
 
+void HTMLParserScriptRunner::RequestForceDeferredScript(
+    ScriptLoader* script_loader) {
+  PendingScript* pending_script =
+      script_loader->TakePendingScript(ScriptSchedulingType::kForceDefer);
+  if (!pending_script)
+    return;
+
+  if (!pending_script->IsReady()) {
+    pending_script->StartStreamingIfPossible();
+  }
+
+  DCHECK(script_loader->IsForceDeferred());
+
+  // Add the element to the end of the list of forced deferred scripts that will
+  // execute when the document has finished parsing associated with the Document
+  // of the parser that created the element.
+  force_deferred_scripts_.push_back(pending_script);
+}
+
 // The initial steps for 'An end tag whose tag name is "script"'
 // <specdef href="https://html.spec.whatwg.org/C/#scriptEndTag">
 // <specdef label="prepare-a-script"
@@ -544,7 +600,11 @@ void HTMLParserScriptRunner::ProcessScriptElementInternal(
       return;
 
     if (script_loader->WillExecuteWhenDocumentFinishedParsing()) {
+      // Developer deferred.
       RequestDeferredScript(script_loader);
+    } else if (script_loader->IsForceDeferred()) {
+      // Force defer this otherwise parser-blocking script.
+      RequestForceDeferredScript(script_loader);
     } else if (script_loader->ReadyToBeParserExecuted()) {
       // <spec label="prepare-a-script" step="26.E">... it's an HTML parser
       // whose script nesting level is not greater than one, ...</spec>
@@ -589,10 +649,48 @@ void HTMLParserScriptRunner::ProcessScriptElementInternal(
   }
 }
 
-void HTMLParserScriptRunner::Trace(blink::Visitor* visitor) {
+void HTMLParserScriptRunner::RecordMetricsAtParseEnd() const {
+  // This method is called just before starting execution of force defer
+  // scripts in order to capture the all force deferred scripts in
+  // |force_deferred_scripts_| before any are popped for execution.
+
+  if (!document_->GetFrame())
+    return;
+
+  if (!force_deferred_scripts_.IsEmpty()) {
+    uint32_t force_deferred_external_script_count = 0;
+    for (const auto& pending_script : force_deferred_scripts_) {
+      if (pending_script->IsExternal())
+        force_deferred_external_script_count++;
+    }
+    if (document_->IsInMainFrame()) {
+      UMA_HISTOGRAM_COUNTS_100("Blink.Script.ForceDeferredScripts.Mainframe",
+                               force_deferred_scripts_.size());
+      UMA_HISTOGRAM_COUNTS_100(
+          "Blink.Script.ForceDeferredScripts.Mainframe.External",
+          force_deferred_external_script_count);
+      if (document_->UkmRecorder()) {
+        ukm::builders::PreviewsDeferAllScript(document_->UkmSourceID())
+            .Setforce_deferred_scripts_mainframe(force_deferred_scripts_.size())
+            .Setforce_deferred_scripts_mainframe_external(
+                force_deferred_external_script_count)
+            .Record(document_->UkmRecorder());
+      }
+    } else {
+      UMA_HISTOGRAM_COUNTS_100("Blink.Script.ForceDeferredScripts.Subframe",
+                               force_deferred_scripts_.size());
+      UMA_HISTOGRAM_COUNTS_100(
+          "Blink.Script.ForceDeferredScripts.Subframe.External",
+          force_deferred_external_script_count);
+    }
+  }
+}
+
+void HTMLParserScriptRunner::Trace(Visitor* visitor) {
   visitor->Trace(document_);
   visitor->Trace(host_);
   visitor->Trace(parser_blocking_script_);
+  visitor->Trace(force_deferred_scripts_);
   visitor->Trace(scripts_to_execute_after_parsing_);
   PendingScriptClient::Trace(visitor);
 }
diff --git a/chromium/third_party/blink/renderer/core/script/html_parser_script_runner.h b/chromium/third_party/blink/renderer/core/script/html_parser_script_runner.h
index f9b1dce95a2..a3f88c0dff3 100644
--- a/chromium/third_party/blink/renderer/core/script/html_parser_script_runner.h
+++ b/chromium/third_party/blink/renderer/core/script/html_parser_script_runner.h
@@ -93,6 +93,8 @@ class HTMLParserScriptRunner final
   void ExecuteScriptsWaitingForResources();
 
   // Invoked when parsing is stopping, to execute any deferred scripts.
+  // This includes forced deferred scripts as well as developer deferred
+  // scripts.
   bool ExecuteScriptsWaitingForParsing();
 
   bool HasParserBlockingScript() const;
@@ -100,7 +102,11 @@ class HTMLParserScriptRunner final
     return !!reentry_permit_->ScriptNestingLevel();
   }
 
-  void Trace(blink::Visitor*) override;
+  // Records metrics related to the parsing phase. To be called when parsing
+  // is preparing to stop but before |ExecuteScriptsWaitingForParsing|.
+  void RecordMetricsAtParseEnd() const;
+
+  void Trace(Visitor*) override;
   const char* NameInHeapSnapshot() const override {
     return "HTMLParserScriptRunner";
   }
@@ -115,6 +121,7 @@ class HTMLParserScriptRunner final
 
   void RequestParsingBlockingScript(ScriptLoader*);
   void RequestDeferredScript(ScriptLoader*);
+  void RequestForceDeferredScript(ScriptLoader*);
 
   // Processes the provided script element, but does not execute any
   // parsing-blocking scripts that may remain after execution.
@@ -129,6 +136,12 @@ class HTMLParserScriptRunner final
 
   void PossiblyFetchBlockedDocWriteScript(PendingScript*);
 
+  // Takes and returns the first PendingScript from |waiting_scripts| if it is
+  // ready for execution. Otherwise, informs it that |this| is a
+  // PendingScriptClient to be informed when it is ready.
+  PendingScript* TryTakeReadyScriptWaitingForParsing(
+      HeapDeque<Member<PendingScript>>* waiting_scripts);
+
   scoped_refptr<HTMLParserReentryPermit> reentry_permit_;
   Member<Document> document_;
   Member<HTMLParserScriptRunnerHost> host_;
@@ -136,6 +149,13 @@ class HTMLParserScriptRunner final
   // https://html.spec.whatwg.org/C/#pending-parsing-blocking-script
   Member<PendingScript> parser_blocking_script_;
 
+  // Scripts that were force deferred by the defer all script optimization.
+  // These scripts will be executed after parsing but before
+  // |scripts_to_execute_after_parsing_|.  This is an ordered list.
+  // https://crbug.com/976061
+  HeapDeque<Member<PendingScript>> force_deferred_scripts_;
+
+  // Scripts that were deferred by the web developer. This is an ordered list.
   // https://html.spec.whatwg.org/C/#list-of-scripts-that-will-execute-when-the-document-has-finished-parsing
   HeapDeque<Member<PendingScript>> scripts_to_execute_after_parsing_;
 
diff --git a/chromium/third_party/blink/renderer/core/script/html_parser_script_runner_host.h b/chromium/third_party/blink/renderer/core/script/html_parser_script_runner_host.h
index dd5f4fbe1c4..1a4770c0a2a 100644
--- a/chromium/third_party/blink/renderer/core/script/html_parser_script_runner_host.h
+++ b/chromium/third_party/blink/renderer/core/script/html_parser_script_runner_host.h
@@ -37,7 +37,7 @@ class PendingScript;
 class CORE_EXPORT HTMLParserScriptRunnerHost : public GarbageCollectedMixin {
  public:
   virtual ~HTMLParserScriptRunnerHost() = default;
-  void Trace(blink::Visitor* visitor) override {}
+  void Trace(Visitor* visitor) override {}
 
   virtual void NotifyScriptLoaded(PendingScript*) = 0;
   virtual HTMLInputStream& InputStream() = 0;
diff --git a/chromium/third_party/blink/renderer/core/script/ignore_destructive_write_count_incrementer.h b/chromium/third_party/blink/renderer/core/script/ignore_destructive_write_count_incrementer.h
index cedad851068..02738ad8bc5 100644
--- a/chromium/third_party/blink/renderer/core/script/ignore_destructive_write_count_incrementer.h
+++ b/chromium/third_party/blink/renderer/core/script/ignore_destructive_write_count_incrementer.h
@@ -28,7 +28,7 @@
 
 #include "base/macros.h"
 #include "third_party/blink/renderer/core/dom/document.h"
-#include "third_party/blink/renderer/platform/wtf/allocator.h"
+#include "third_party/blink/renderer/platform/wtf/allocator/allocator.h"
 
 namespace blink {
 
diff --git a/chromium/third_party/blink/renderer/core/script/import_map.cc b/chromium/third_party/blink/renderer/core/script/import_map.cc
index fceaddd75a9..c78d79dda49 100644
--- a/chromium/third_party/blink/renderer/core/script/import_map.cc
+++ b/chromium/third_party/blink/renderer/core/script/import_map.cc
@@ -187,7 +187,7 @@ ImportMap* ImportMap::Create(const Modulator& modulator_for_built_in_modules,
       values.clear();
     }
     if (values.size() == 2) {
-      if (blink::layered_api::GetBuiltinPath(values[0]).IsNull()) {
+      if (layered_api::GetBuiltinPath(values[0]).IsNull()) {
         AddIgnoredValueMessage(
             logger, entry.first,
             "Fallback from a non-builtin URL is not yet supported.");
@@ -282,8 +282,8 @@ base::Optional<KURL> ImportMap::Resolve(const ParsedSpecifier& parsed_specifier,
 
   for (const KURL& value : matched->value) {
     const KURL complete_url = postfix.IsEmpty() ? value : KURL(value, postfix);
-    if (blink::layered_api::ResolveFetchingURL(*modulator_for_built_in_modules_,
-                                               complete_url)
+    if (layered_api::ResolveFetchingURL(*modulator_for_built_in_modules_,
+                                        complete_url)
             .IsValid()) {
       *debug_message = "Import Map: \"" + key + "\" matches with \"" +
                        matched->key + "\" and is mapped to " +
diff --git a/chromium/third_party/blink/renderer/core/script/js_module_script.cc b/chromium/third_party/blink/renderer/core/script/js_module_script.cc
index d53409bf7c6..8b12c6ac851 100644
--- a/chromium/third_party/blink/renderer/core/script/js_module_script.cc
+++ b/chromium/third_party/blink/renderer/core/script/js_module_script.cc
@@ -6,8 +6,6 @@
 
 #include "third_party/blink/renderer/bindings/core/v8/script_value.h"
 #include "third_party/blink/renderer/core/script/module_record_resolver.h"
-#include "third_party/blink/renderer/core/workers/worker_global_scope.h"
-#include "third_party/blink/renderer/core/workers/worker_reporting_proxy.h"
 #include "third_party/blink/renderer/platform/bindings/script_state.h"
 #include "v8/include/v8.h"
 
@@ -166,21 +164,6 @@ JSModuleScript::JSModuleScript(Modulator* settings_object,
       start_position_(start_position),
       produce_cache_data_(produce_cache_data) {}
 
-void JSModuleScript::RunScriptOnWorker(WorkerGlobalScope& worker_global_scope) {
-  DCHECK(worker_global_scope.IsContextThread());
-
-  WorkerReportingProxy& worker_reporting_proxy =
-      worker_global_scope.ReportingProxy();
-
-  worker_reporting_proxy.WillEvaluateModuleScript();
-  // This |error| is always null because the second argument is |kReport|.
-  // TODO(nhiroki): Catch an error when an evaluation error happens.
-  // (https://crbug.com/680046)
-  ScriptValue error = SettingsObject()->ExecuteModule(
-      this, Modulator::CaptureEvalErrorFlag::kReport);
-  worker_reporting_proxy.DidEvaluateModuleScript(error.IsEmpty());
-}
-
 String JSModuleScript::InlineSourceTextForCSP() const {
   return source_text_.ToString();
 }
@@ -199,7 +182,7 @@ void JSModuleScript::ProduceCache() {
   produce_cache_data_ = nullptr;
 }
 
-void JSModuleScript::Trace(blink::Visitor* visitor) {
+void JSModuleScript::Trace(Visitor* visitor) {
   visitor->Trace(produce_cache_data_);
   ModuleScript::Trace(visitor);
 }
diff --git a/chromium/third_party/blink/renderer/core/script/js_module_script.h b/chromium/third_party/blink/renderer/core/script/js_module_script.h
index db070c73340..61089f896de 100644
--- a/chromium/third_party/blink/renderer/core/script/js_module_script.h
+++ b/chromium/third_party/blink/renderer/core/script/js_module_script.h
@@ -57,7 +57,7 @@ class CORE_EXPORT JSModuleScript final : public ModuleScript,
 
   void ProduceCache() override;
 
-  void Trace(blink::Visitor*) override;
+  void Trace(Visitor*) override;
   const char* NameInHeapSnapshot() const override { return "JSModuleScript"; }
 
  private:
@@ -74,7 +74,6 @@ class CORE_EXPORT JSModuleScript final : public ModuleScript,
       ModuleRecordProduceCacheData* produce_cache_data);
 
   const TextPosition& StartPosition() const { return start_position_; }
-  void RunScriptOnWorker(WorkerGlobalScope&) override;
   String InlineSourceTextForCSP() const override;
 
   // For CSP check.
diff --git a/chromium/third_party/blink/renderer/core/script/layered_api_module.h b/chromium/third_party/blink/renderer/core/script/layered_api_module.h
index 28809a991c0..7dd7d687dab 100644
--- a/chromium/third_party/blink/renderer/core/script/layered_api_module.h
+++ b/chromium/third_party/blink/renderer/core/script/layered_api_module.h
@@ -15,7 +15,10 @@ namespace layered_api {
 
 enum class Module {
   kBlank,
-  kVirtualScroller,
+  kElementsInternal,
+  kElementsSwitch,
+  kElementsToast,
+  kElementsVirtualScroller,
   kKvStorage,
 };
 
diff --git a/chromium/third_party/blink/renderer/core/script/layered_api_resources.h b/chromium/third_party/blink/renderer/core/script/layered_api_resources.h
index f822934e6ff..98be4b31e1a 100644
--- a/chromium/third_party/blink/renderer/core/script/layered_api_resources.h
+++ b/chromium/third_party/blink/renderer/core/script/layered_api_resources.h
@@ -29,6 +29,35 @@ struct LayeredAPIResource {
 const LayeredAPIResource kLayeredAPIResources[] = {
     {"blank/index.mjs", IDR_LAYERED_API_BLANK_INDEX_MJS, Module::kBlank},
 
+    {"elements/internal/reflection.mjs",
+     IDR_LAYERED_API_ELEMENTS_INTERNAL_REFLECTION_MJS,
+     Module::kElementsInternal},
+
+    {"elements/switch/face_utils.mjs",
+     IDR_LAYERED_API_ELEMENTS_SWITCH_FACE_UTILS_MJS, Module::kElementsSwitch},
+    {"elements/switch/index.mjs", IDR_LAYERED_API_ELEMENTS_SWITCH_INDEX_MJS,
+     Module::kElementsSwitch},
+    {"elements/switch/style.mjs", IDR_LAYERED_API_ELEMENTS_SWITCH_STYLE_MJS,
+     Module::kElementsSwitch},
+    {"elements/switch/track.mjs", IDR_LAYERED_API_ELEMENTS_SWITCH_TRACK_MJS,
+     Module::kElementsSwitch},
+
+    {"elements/toast/index.mjs", IDR_LAYERED_API_ELEMENTS_TOAST_INDEX_MJS,
+     Module::kElementsToast},
+
+    {"elements/virtual-scroller/find-element.mjs",
+     IDR_LAYERED_API_ELEMENTS_VIRTUAL_SCROLLER_FIND_ELEMENT_MJS,
+     Module::kElementsVirtualScroller},
+    {"elements/virtual-scroller/index.mjs",
+     IDR_LAYERED_API_ELEMENTS_VIRTUAL_SCROLLER_INDEX_MJS,
+     Module::kElementsVirtualScroller},
+    {"elements/virtual-scroller/sets.mjs",
+     IDR_LAYERED_API_ELEMENTS_VIRTUAL_SCROLLER_SETS_MJS,
+     Module::kElementsVirtualScroller},
+    {"elements/virtual-scroller/visibility-manager.mjs",
+     IDR_LAYERED_API_ELEMENTS_VIRTUAL_SCROLLER_VISIBILITY_MANAGER_MJS,
+     Module::kElementsVirtualScroller},
+
     {"kv-storage/async_iterator.mjs",
      IDR_LAYERED_API_KV_STORAGE_ASYNC_ITERATOR_MJS, Module::kKvStorage},
     {"kv-storage/idb_utils.mjs", IDR_LAYERED_API_KV_STORAGE_IDB_UTILS_MJS,
@@ -36,28 +65,6 @@ const LayeredAPIResource kLayeredAPIResources[] = {
     {"kv-storage/index.mjs", IDR_LAYERED_API_KV_STORAGE_INDEX_MJS,
      Module::kKvStorage},
 
-    {"virtual-scroller/index.mjs", IDR_LAYERED_API_VIRTUAL_SCROLLER_INDEX_MJS,
-     Module::kVirtualScroller},
-    {"virtual-scroller/item-source.mjs",
-     IDR_LAYERED_API_VIRTUAL_SCROLLER_ITEM_SOURCE_MJS,
-     Module::kVirtualScroller},
-    {"virtual-scroller/virtual-repeater.mjs",
-     IDR_LAYERED_API_VIRTUAL_SCROLLER_VIRTUAL_REPEATER_MJS,
-     Module::kVirtualScroller},
-    {"virtual-scroller/virtual-scroller.mjs",
-     IDR_LAYERED_API_VIRTUAL_SCROLLER_VIRTUAL_SCROLLER_MJS,
-     Module::kVirtualScroller},
-
-    {"virtual-scroller/layouts/layout-1d-base.mjs",
-     IDR_LAYERED_API_VIRTUAL_SCROLLER_LAYOUTS_LAYOUT_1D_BASE_MJS,
-     Module::kVirtualScroller},
-    {"virtual-scroller/layouts/layout-1d-grid.mjs",
-     IDR_LAYERED_API_VIRTUAL_SCROLLER_LAYOUTS_LAYOUT_1D_GRID_MJS,
-     Module::kVirtualScroller},
-    {"virtual-scroller/layouts/layout-1d.mjs",
-     IDR_LAYERED_API_VIRTUAL_SCROLLER_LAYOUTS_LAYOUT_1D_MJS,
-     Module::kVirtualScroller},
-
 };
 
 }  // namespace
diff --git a/chromium/third_party/blink/renderer/core/script/layered_api_test.cc b/chromium/third_party/blink/renderer/core/script/layered_api_test.cc
index 28ac45737df..f318f7fc807 100644
--- a/chromium/third_party/blink/renderer/core/script/layered_api_test.cc
+++ b/chromium/third_party/blink/renderer/core/script/layered_api_test.cc
@@ -16,9 +16,7 @@ namespace {
 class LayeredAPITestModulator final : public DummyModulator {
  public:
   bool BuiltInModuleInfraEnabled() const override { return true; }
-  bool BuiltInModuleEnabled(blink::layered_api::Module) const override {
-    return true;
-  }
+  bool BuiltInModuleEnabled(layered_api::Module) const override { return true; }
 };
 
 class LayeredAPITest : public testing::Test {
diff --git a/chromium/third_party/blink/renderer/core/script/mock_script_element_base.h b/chromium/third_party/blink/renderer/core/script/mock_script_element_base.h
index 2afb66aefb4..2722f3a7971 100644
--- a/chromium/third_party/blink/renderer/core/script/mock_script_element_base.h
+++ b/chromium/third_party/blink/renderer/core/script/mock_script_element_base.h
@@ -55,9 +55,7 @@ class MockScriptElementBase
                void(HTMLScriptElementOrSVGScriptElement&));
   MOCK_CONST_METHOD0(Loader, ScriptLoader*());
 
-  void Trace(blink::Visitor* visitor) override {
-    ScriptElementBase::Trace(visitor);
-  }
+  void Trace(Visitor* visitor) override { ScriptElementBase::Trace(visitor); }
 };
 
 }  // namespace blink
diff --git a/chromium/third_party/blink/renderer/core/script/modulator.h b/chromium/third_party/blink/renderer/core/script/modulator.h
index 350858d9972..9f67b4e5afa 100644
--- a/chromium/third_party/blink/renderer/core/script/modulator.h
+++ b/chromium/third_party/blink/renderer/core/script/modulator.h
@@ -6,7 +6,7 @@
 #define THIRD_PARTY_BLINK_RENDERER_CORE_SCRIPT_MODULATOR_H_
 
 #include "base/single_thread_task_runner.h"
-#include "services/network/public/mojom/referrer_policy.mojom-shared.h"
+#include "services/network/public/mojom/referrer_policy.mojom-blink.h"
 #include "third_party/blink/public/platform/web_url_request.h"
 #include "third_party/blink/renderer/bindings/core/v8/module_record.h"
 #include "third_party/blink/renderer/bindings/core/v8/sanitize_script_errors.h"
@@ -44,7 +44,7 @@ class CORE_EXPORT SingleModuleClient
       public NameClient {
  public:
   virtual ~SingleModuleClient() = default;
-  virtual void Trace(blink::Visitor* visitor) {}
+  virtual void Trace(Visitor* visitor) {}
   const char* NameInHeapSnapshot() const override {
     return "SingleModuleClient";
   }
@@ -59,7 +59,7 @@ class CORE_EXPORT ModuleTreeClient
       public NameClient {
  public:
   virtual ~ModuleTreeClient() = default;
-  virtual void Trace(blink::Visitor* visitor) {}
+  virtual void Trace(Visitor* visitor) {}
   const char* NameInHeapSnapshot() const override { return "ModuleTreeClient"; }
 
   virtual void NotifyModuleTreeLoadFinished(ModuleScript*) = 0;
@@ -107,7 +107,7 @@ class CORE_EXPORT Modulator : public GarbageCollectedFinalized<Modulator>,
   static void SetModulator(ScriptState*, Modulator*);
   static void ClearModulator(ScriptState*);
 
-  void Trace(blink::Visitor* visitor) override {}
+  void Trace(Visitor* visitor) override {}
   const char* NameInHeapSnapshot() const override { return "Modulator"; }
 
   virtual ModuleRecordResolver* GetModuleRecordResolver() = 0;
@@ -122,8 +122,8 @@ class CORE_EXPORT Modulator : public GarbageCollectedFinalized<Modulator>,
   virtual bool IsScriptingDisabled() const = 0;
 
   virtual bool BuiltInModuleInfraEnabled() const = 0;
-  virtual bool BuiltInModuleEnabled(blink::layered_api::Module) const = 0;
-  virtual void BuiltInModuleUseCount(blink::layered_api::Module) const = 0;
+  virtual bool BuiltInModuleEnabled(layered_api::Module) const = 0;
+  virtual void BuiltInModuleUseCount(layered_api::Module) const = 0;
 
   // https://html.spec.whatwg.org/C/#fetch-a-module-script-tree
   // https://html.spec.whatwg.org/C/#fetch-a-module-worker-script-tree
diff --git a/chromium/third_party/blink/renderer/core/script/modulator_impl_base.cc b/chromium/third_party/blink/renderer/core/script/modulator_impl_base.cc
index 441862b5a36..a3bcbe4b6ae 100644
--- a/chromium/third_party/blink/renderer/core/script/modulator_impl_base.cc
+++ b/chromium/third_party/blink/renderer/core/script/modulator_impl_base.cc
@@ -7,7 +7,6 @@
 #include "third_party/blink/public/platform/task_type.h"
 #include "third_party/blink/renderer/bindings/core/v8/script_promise_resolver.h"
 #include "third_party/blink/renderer/core/execution_context/execution_context.h"
-#include "third_party/blink/renderer/core/frame/use_counter.h"
 #include "third_party/blink/renderer/core/loader/modulescript/module_script_fetch_request.h"
 #include "third_party/blink/renderer/core/loader/modulescript/module_tree_linker.h"
 #include "third_party/blink/renderer/core/loader/modulescript/module_tree_linker_registry.h"
@@ -18,6 +17,7 @@
 #include "third_party/blink/renderer/core/script/module_record_resolver_impl.h"
 #include "third_party/blink/renderer/core/script/parsed_specifier.h"
 #include "third_party/blink/renderer/platform/bindings/v8_throw_exception.h"
+#include "third_party/blink/renderer/platform/instrumentation/use_counter.h"
 #include "third_party/blink/renderer/platform/runtime_enabled_features.h"
 
 namespace blink {
@@ -52,33 +52,49 @@ bool ModulatorImplBase::BuiltInModuleInfraEnabled() const {
       GetExecutionContext());
 }
 
-bool ModulatorImplBase::BuiltInModuleEnabled(
-    blink::layered_api::Module module) const {
+bool ModulatorImplBase::BuiltInModuleEnabled(layered_api::Module module) const {
   DCHECK(BuiltInModuleInfraEnabled());
+  if (RuntimeEnabledFeatures::BuiltInModuleAllEnabled())
+    return true;
   switch (module) {
-    case blink::layered_api::Module::kBlank:
+    case layered_api::Module::kBlank:
       return true;
-    case blink::layered_api::Module::kVirtualScroller:
+    case layered_api::Module::kKvStorage:
+      return RuntimeEnabledFeatures::BuiltInModuleKvStorageEnabled(
+          GetExecutionContext());
+    case layered_api::Module::kElementsInternal:
+      // Union of conditions of KElementsSwitch and kElementsToast.
+      return RuntimeEnabledFeatures::BuiltInModuleSwitchElementEnabled();
+    case layered_api::Module::kElementsSwitch:
+      return RuntimeEnabledFeatures::BuiltInModuleSwitchElementEnabled();
+    case layered_api::Module::kElementsToast:
       return RuntimeEnabledFeatures::BuiltInModuleAllEnabled();
-    case blink::layered_api::Module::kKvStorage:
-      return RuntimeEnabledFeatures::BuiltInModuleAllEnabled() ||
-             RuntimeEnabledFeatures::BuiltInModuleKvStorageEnabled(
-                 GetExecutionContext());
+    case layered_api::Module::kElementsVirtualScroller:
+      return false;
   }
 }
 
 void ModulatorImplBase::BuiltInModuleUseCount(
-    blink::layered_api::Module module) const {
+    layered_api::Module module) const {
   DCHECK(BuiltInModuleInfraEnabled());
   DCHECK(BuiltInModuleEnabled(module));
   switch (module) {
-    case blink::layered_api::Module::kBlank:
+    case layered_api::Module::kBlank:
       break;
-    case blink::layered_api::Module::kVirtualScroller:
+    case layered_api::Module::kElementsInternal:
+      break;
+    case layered_api::Module::kElementsSwitch:
+      UseCounter::Count(GetExecutionContext(),
+                        WebFeature::kBuiltInModuleSwitchImported);
+      break;
+    case layered_api::Module::kElementsToast:
+      UseCounter::Count(GetExecutionContext(), WebFeature::kBuiltInModuleToast);
+      break;
+    case layered_api::Module::kElementsVirtualScroller:
       UseCounter::Count(GetExecutionContext(),
                         WebFeature::kBuiltInModuleVirtualScroller);
       break;
-    case blink::layered_api::Module::kKvStorage:
+    case layered_api::Module::kKvStorage:
       UseCounter::Count(GetExecutionContext(),
                         WebFeature::kBuiltInModuleKvStorage);
       break;
@@ -96,32 +112,9 @@ void ModulatorImplBase::FetchTree(
     const ScriptFetchOptions& options,
     ModuleScriptCustomFetchType custom_fetch_type,
     ModuleTreeClient* client) {
-  // <spec label="fetch-a-module-script-tree" step="2">Perform the internal
-  // module script graph fetching procedure given url, settings object,
-  // destination, options, settings object, visited set, "client", and with the
-  // top-level module fetch flag set. If the caller of this algorithm specified
-  // custom perform the fetch steps, pass those along as well.</spec>
-
-  // <spec label="fetch-a-module-worker-script-tree" step="3">Perform the
-  // internal module script graph fetching procedure given url, fetch client
-  // settings object, destination, options, module map settings object, visited
-  // set, "client", and with the top-level module fetch flag set. If the caller
-  // of this algorithm specified custom perform the fetch steps, pass those
-  // along as well.</spec>
-
   ModuleTreeLinker::Fetch(url, fetch_client_settings_object_fetcher,
                           destination, options, this, custom_fetch_type,
                           tree_linker_registry_, client);
-
-  // <spec label="fetch-a-module-script-tree" step="3">When the internal module
-  // script graph fetching procedure asynchronously completes with result,
-  // asynchronously complete this algorithm with result.</spec>
-
-  // <spec label="fetch-a-module-worker-script-tree" step="4">When the internal
-  // module script graph fetching procedure asynchronously completes with
-  // result, asynchronously complete this algorithm with result.</spec>
-
-  // Note: We delegate to ModuleTreeLinker to notify ModuleTreeClient.
 }
 
 void ModulatorImplBase::FetchDescendantsForInlineScript(
@@ -265,14 +258,14 @@ ModuleImportMeta ModulatorImplBase::HostGetImportMetaProperties(
     ModuleRecord record) const {
   // <spec step="1">Let module script be moduleRecord.[[HostDefined]].</spec>
   const ModuleScript* module_script =
-      module_record_resolver_->GetHostDefined(record);
+      module_record_resolver_->GetModuleScriptFromModuleRecord(record);
   DCHECK(module_script);
 
-  // <spec step="2">Let urlString be module script's base URL,
+  // <spec step="3">Let urlString be module script's base URL,
   // serialized.</spec>
   String url_string = module_script->BaseURL().GetString();
 
-  // <spec step="3">Return « Record { [[Key]]: "url", [[Value]]: urlString }
+  // <spec step="4">Return « Record { [[Key]]: "url", [[Value]]: urlString }
   // ».</spec>
   return ModuleImportMeta(url_string);
 }
@@ -416,7 +409,7 @@ ScriptValue ModulatorImplBase::ExecuteModule(
   return ScriptValue();
 }
 
-void ModulatorImplBase::Trace(blink::Visitor* visitor) {
+void ModulatorImplBase::Trace(Visitor* visitor) {
   visitor->Trace(script_state_);
   visitor->Trace(map_);
   visitor->Trace(tree_linker_registry_);
diff --git a/chromium/third_party/blink/renderer/core/script/modulator_impl_base.h b/chromium/third_party/blink/renderer/core/script/modulator_impl_base.h
index 53780b19229..6721f1cb8af 100644
--- a/chromium/third_party/blink/renderer/core/script/modulator_impl_base.h
+++ b/chromium/third_party/blink/renderer/core/script/modulator_impl_base.h
@@ -27,7 +27,7 @@ class ScriptState;
 class ModulatorImplBase : public Modulator {
  public:
   ~ModulatorImplBase() override;
-  void Trace(blink::Visitor*) override;
+  void Trace(Visitor*) override;
 
  protected:
   explicit ModulatorImplBase(ScriptState*);
@@ -42,8 +42,8 @@ class ModulatorImplBase : public Modulator {
   bool IsScriptingDisabled() const override;
 
   bool BuiltInModuleInfraEnabled() const override;
-  bool BuiltInModuleEnabled(blink::layered_api::Module) const override;
-  void BuiltInModuleUseCount(blink::layered_api::Module) const override;
+  bool BuiltInModuleEnabled(layered_api::Module) const override;
+  void BuiltInModuleUseCount(layered_api::Module) const override;
 
   ModuleRecordResolver* GetModuleRecordResolver() override {
     return module_record_resolver_.Get();
diff --git a/chromium/third_party/blink/renderer/core/script/module_map.cc b/chromium/third_party/blink/renderer/core/script/module_map.cc
index f8fc91cf97f..d38ecfd0038 100644
--- a/chromium/third_party/blink/renderer/core/script/module_map.cc
+++ b/chromium/third_party/blink/renderer/core/script/module_map.cc
@@ -25,7 +25,7 @@ class ModuleMap::Entry final : public GarbageCollectedFinalized<Entry>,
   explicit Entry(ModuleMap*);
   ~Entry() override {}
 
-  void Trace(blink::Visitor*) override;
+  void Trace(Visitor*) override;
   const char* NameInHeapSnapshot() const override { return "ModuleMap::Entry"; }
 
   // Notify fetched |m_moduleScript| to the client asynchronously.
@@ -53,7 +53,7 @@ ModuleMap::Entry::Entry(ModuleMap* map) : map_(map) {
   DCHECK(map_);
 }
 
-void ModuleMap::Entry::Trace(blink::Visitor* visitor) {
+void ModuleMap::Entry::Trace(Visitor* visitor) {
   visitor->Trace(module_script_);
   visitor->Trace(map_);
   visitor->Trace(clients_);
@@ -100,7 +100,7 @@ ModuleMap::ModuleMap(Modulator* modulator)
   DCHECK(modulator);
 }
 
-void ModuleMap::Trace(blink::Visitor* visitor) {
+void ModuleMap::Trace(Visitor* visitor) {
   visitor->Trace(map_);
   visitor->Trace(modulator_);
   visitor->Trace(loader_registry_);
@@ -137,7 +137,7 @@ void ModuleMap::FetchSingleModuleScript(
   // <spec step="3">If moduleMap[url] exists, asynchronously complete this
   // algorithm with moduleMap[url], and abort these steps.</spec>
   //
-  // <spec step="12">Set moduleMap[url] to module script, and asynchronously
+  // <spec step="14">Set moduleMap[url] to module script, and asynchronously
   // complete this algorithm with module script.</spec>
   if (client)
     entry->AddClient(client);
diff --git a/chromium/third_party/blink/renderer/core/script/module_map.h b/chromium/third_party/blink/renderer/core/script/module_map.h
index fa0018a3cf9..46d98e67aa3 100644
--- a/chromium/third_party/blink/renderer/core/script/module_map.h
+++ b/chromium/third_party/blink/renderer/core/script/module_map.h
@@ -33,7 +33,7 @@ class CORE_EXPORT ModuleMap final : public GarbageCollected<ModuleMap>,
  public:
   explicit ModuleMap(Modulator*);
 
-  void Trace(blink::Visitor*);
+  void Trace(Visitor*);
   const char* NameInHeapSnapshot() const override { return "ModuleMap"; }
 
   // https://html.spec.whatwg.org/C/#fetch-a-single-module-script
diff --git a/chromium/third_party/blink/renderer/core/script/module_map_test.cc b/chromium/third_party/blink/renderer/core/script/module_map_test.cc
index da2f4ab72f2..6df17a931d6 100644
--- a/chromium/third_party/blink/renderer/core/script/module_map_test.cc
+++ b/chromium/third_party/blink/renderer/core/script/module_map_test.cc
@@ -30,7 +30,7 @@ class TestSingleModuleClient final : public SingleModuleClient {
   TestSingleModuleClient() = default;
   ~TestSingleModuleClient() override {}
 
-  void Trace(blink::Visitor* visitor) override {
+  void Trace(Visitor* visitor) override {
     visitor->Trace(module_script_);
     SingleModuleClient::Trace(visitor);
   }
@@ -64,7 +64,8 @@ class TestModuleRecordResolver final : public ModuleRecordResolver {
     FAIL() << "UnregisterModuleScript shouldn't be called in ModuleMapTest";
   }
 
-  const ModuleScript* GetHostDefined(const ModuleRecord&) const override {
+  const ModuleScript* GetModuleScriptFromModuleRecord(
+      const ModuleRecord&) const override {
     NOTREACHED();
     return nullptr;
   }
@@ -87,7 +88,7 @@ class ModuleMapTestModulator final : public DummyModulator {
   explicit ModuleMapTestModulator(ScriptState*);
   ~ModuleMapTestModulator() override {}
 
-  void Trace(blink::Visitor*) override;
+  void Trace(Visitor*) override;
 
   TestModuleRecordResolver* GetTestModuleRecordResolver() {
     return resolver_.Get();
@@ -117,12 +118,12 @@ class ModuleMapTestModulator final : public DummyModulator {
       TestRequest* test_request = MakeGarbageCollected<TestRequest>(
           ModuleScriptCreationParams(
               request.Url(), ParkableString(String("").ReleaseImpl()), nullptr,
-              request.GetResourceRequest().GetFetchCredentialsMode()),
+              request.GetResourceRequest().GetCredentialsMode()),
           client);
       modulator_->test_requests_.push_back(test_request);
     }
     String DebugName() const override { return "TestModuleScriptFetcher"; }
-    void Trace(blink::Visitor* visitor) override {
+    void Trace(Visitor* visitor) override {
       ModuleScriptFetcher::Trace(visitor);
       visitor->Trace(modulator_);
     }
@@ -152,7 +153,7 @@ class ModuleMapTestModulator final : public DummyModulator {
       client_->NotifyFetchFinished(*params_,
                                    HeapVector<Member<ConsoleMessage>>());
     }
-    void Trace(blink::Visitor* visitor) { visitor->Trace(client_); }
+    void Trace(Visitor* visitor) { visitor->Trace(client_); }
 
    private:
     base::Optional<ModuleScriptCreationParams> params_;
@@ -168,7 +169,7 @@ ModuleMapTestModulator::ModuleMapTestModulator(ScriptState* script_state)
     : script_state_(script_state),
       resolver_(MakeGarbageCollected<TestModuleRecordResolver>()) {}
 
-void ModuleMapTestModulator::Trace(blink::Visitor* visitor) {
+void ModuleMapTestModulator::Trace(Visitor* visitor) {
   visitor->Trace(test_requests_);
   visitor->Trace(script_state_);
   visitor->Trace(resolver_);
@@ -198,8 +199,7 @@ class ModuleMapTest : public PageTestBase {
 
 void ModuleMapTest::SetUp() {
   PageTestBase::SetUp(IntSize(500, 500));
-  GetDocument().SetURL(KURL("https://example.com"));
-  GetDocument().SetSecurityOrigin(SecurityOrigin::Create(GetDocument().Url()));
+  NavigateTo(KURL("https://example.com"));
   modulator_ = MakeGarbageCollected<ModuleMapTestModulator>(
       ToScriptStateForMainWorld(&GetFrame()));
   map_ = MakeGarbageCollected<ModuleMap>(modulator_);
diff --git a/chromium/third_party/blink/renderer/core/script/module_pending_script.cc b/chromium/third_party/blink/renderer/core/script/module_pending_script.cc
index cfe0735ec4f..29449ea2056 100644
--- a/chromium/third_party/blink/renderer/core/script/module_pending_script.cc
+++ b/chromium/third_party/blink/renderer/core/script/module_pending_script.cc
@@ -31,7 +31,7 @@ void ModulePendingScriptTreeClient::NotifyModuleTreeLoadFinished(
     pending_script_->NotifyModuleTreeLoadFinished();
 }
 
-void ModulePendingScriptTreeClient::Trace(blink::Visitor* visitor) {
+void ModulePendingScriptTreeClient::Trace(Visitor* visitor) {
   visitor->Trace(module_script_);
   visitor->Trace(pending_script_);
   ModuleTreeClient::Trace(visitor);
@@ -54,7 +54,7 @@ void ModulePendingScript::DisposeInternal() {
   module_tree_client_ = nullptr;
 }
 
-void ModulePendingScript::Trace(blink::Visitor* visitor) {
+void ModulePendingScript::Trace(Visitor* visitor) {
   visitor->Trace(module_tree_client_);
   PendingScript::Trace(visitor);
 }
diff --git a/chromium/third_party/blink/renderer/core/script/module_pending_script.h b/chromium/third_party/blink/renderer/core/script/module_pending_script.h
index b0253af0d6c..230d4632c4d 100644
--- a/chromium/third_party/blink/renderer/core/script/module_pending_script.h
+++ b/chromium/third_party/blink/renderer/core/script/module_pending_script.h
@@ -29,7 +29,7 @@ class ModulePendingScriptTreeClient final : public ModuleTreeClient {
 
   ModuleScript* GetModuleScript() const { return module_script_; }
 
-  void Trace(blink::Visitor*) override;
+  void Trace(Visitor*) override;
 
  private:
   // Implements ModuleTreeClient
@@ -55,7 +55,7 @@ class CORE_EXPORT ModulePendingScript : public PendingScript {
     return module_tree_client_->GetModuleScript();
   }
 
-  void Trace(blink::Visitor*) override;
+  void Trace(Visitor*) override;
 
  private:
   // PendingScript
diff --git a/chromium/third_party/blink/renderer/core/script/module_record_resolver.h b/chromium/third_party/blink/renderer/core/script/module_record_resolver.h
index fb075478d8f..5fb8d6c3b7f 100644
--- a/chromium/third_party/blink/renderer/core/script/module_record_resolver.h
+++ b/chromium/third_party/blink/renderer/core/script/module_record_resolver.h
@@ -26,7 +26,7 @@ class CORE_EXPORT ModuleRecordResolver
     : public GarbageCollectedFinalized<ModuleRecordResolver> {
  public:
   virtual ~ModuleRecordResolver() = default;
-  virtual void Trace(blink::Visitor* visitor) {}
+  virtual void Trace(Visitor* visitor) {}
 
   // Notifies the ModuleRecordResolver that a ModuleScript exists.
   // This hook gives a chance for the resolver impl to populate module record
@@ -36,8 +36,8 @@ class CORE_EXPORT ModuleRecordResolver
   // Notifies the ModuleRecordResolver to clear its ModuleScript mapping.
   virtual void UnregisterModuleScript(const ModuleScript*) = 0;
 
-  // Corresponds to the spec concept "[[HostDefined]]".
-  virtual const ModuleScript* GetHostDefined(const ModuleRecord&) const = 0;
+  virtual const ModuleScript* GetModuleScriptFromModuleRecord(
+      const ModuleRecord&) const = 0;
 
   // Implements "Runtime Semantics: HostResolveImportedModule"
   // https://tc39.github.io/ecma262/#sec-hostresolveimportedmodule
diff --git a/chromium/third_party/blink/renderer/core/script/module_record_resolver_impl.cc b/chromium/third_party/blink/renderer/core/script/module_record_resolver_impl.cc
index 212ee50da5e..46b15431539 100644
--- a/chromium/third_party/blink/renderer/core/script/module_record_resolver_impl.cc
+++ b/chromium/third_party/blink/renderer/core/script/module_record_resolver_impl.cc
@@ -40,7 +40,7 @@ void ModuleRecordResolverImpl::UnregisterModuleScript(
   record_to_module_script_map_.erase(module_script->Record());
 }
 
-const ModuleScript* ModuleRecordResolverImpl::GetHostDefined(
+const ModuleScript* ModuleRecordResolverImpl::GetModuleScriptFromModuleRecord(
     const ModuleRecord& record) const {
   const auto it = record_to_module_script_map_.find(record);
   CHECK_NE(it, record_to_module_script_map_.end())
@@ -58,38 +58,47 @@ ModuleRecord ModuleRecordResolverImpl::Resolve(
     ExceptionState& exception_state) {
   DVLOG(1) << "ModuleRecordResolverImpl::resolve(specifier=\"" << specifier
            << ", referrer.hash=" << ModuleRecordHash::GetHash(referrer) << ")";
+  // <spec step="3">If referencingScriptOrModule is not null, then:</spec>
+  //
+  // Currently this function implements the spec before
+  // https://github.com/tc39/proposal-dynamic-import is applied, i.e. where
+  // |referencingScriptOrModule| was always a non-null module script.
 
-  // <spec step="1">Let referencing script be
-  // referencingScriptOrModule.[[HostDefined]].</spec>
-  const ModuleScript* referrer_module = GetHostDefined(referrer);
-
-  // <spec step="2">Let moduleMap be referencing script's settings object's
-  // module map.</spec>
+  // <spec step="3.2">Set settings object to referencing script's settings
+  // object.</spec>
   //
-  // Note: Blink finds out "module script's settings object"
-  // (Modulator) from context where HostResolveImportedModule was called.
+  // <spec step="4">Let moduleMap be settings object's module map.</spec>
+  //
+  // These are |modulator_| and |this|, respectively, because module script's
+  // settings object is always the current settings object in Blink.
+
+  // <spec step="3.1">Let referencing script be
+  // referencingScriptOrModule.[[HostDefined]].</spec>
+  const ModuleScript* referrer_module =
+      GetModuleScriptFromModuleRecord(referrer);
 
-  // <spec step="3">Let url be the result of resolving a module specifier given
-  // referencing script's base URL and specifier.</spec>
+  // <spec step="3.3">Set base URL to referencing script's base URL.</spec>
+  // <spec step="5">Let url be the result of resolving a module specifier given
+  // base URL and specifier.</spec>
   KURL url = referrer_module->ResolveModuleSpecifier(specifier);
 
-  // <spec step="4">Assert: url is never failure, because resolving a module
+  // <spec step="6">Assert: url is never failure, because resolving a module
   // specifier must have been previously successful with these same two
-  // arguments.</spec>
+  // arguments ...</spec>
   DCHECK(url.IsValid());
 
-  // <spec step="5">Let resolved module script be moduleMap[url]. (This entry
+  // <spec step="7">Let resolved module script be moduleMap[url]. (This entry
   // must exist for us to have gotten to this point.)</spec>
   ModuleScript* module_script = modulator_->GetFetchedModuleScript(url);
 
-  // <spec step="6">Assert: resolved module script is a module script (i.e., is
+  // <spec step="8">Assert: resolved module script is a module script (i.e., is
   // not null or "fetching").</spec>
   //
-  // <spec step="7">Assert: resolved module script's record is not null.</spec>
+  // <spec step="9">Assert: resolved module script's record is not null.</spec>
   DCHECK(module_script);
   CHECK(!module_script->Record().IsNull());
 
-  // <spec step="8">Return resolved module script's record.</spec>
+  // <spec step="10">Return resolved module script's record.</spec>
   return module_script->Record();
 }
 
@@ -99,7 +108,7 @@ void ModuleRecordResolverImpl::ContextDestroyed(ExecutionContext*) {
   record_to_module_script_map_.clear();
 }
 
-void ModuleRecordResolverImpl::Trace(blink::Visitor* visitor) {
+void ModuleRecordResolverImpl::Trace(Visitor* visitor) {
   ModuleRecordResolver::Trace(visitor);
   ContextLifecycleObserver::Trace(visitor);
   visitor->Trace(record_to_module_script_map_);
diff --git a/chromium/third_party/blink/renderer/core/script/module_record_resolver_impl.h b/chromium/third_party/blink/renderer/core/script/module_record_resolver_impl.h
index ecd381f27e3..ee9ec555b52 100644
--- a/chromium/third_party/blink/renderer/core/script/module_record_resolver_impl.h
+++ b/chromium/third_party/blink/renderer/core/script/module_record_resolver_impl.h
@@ -30,7 +30,7 @@ class CORE_EXPORT ModuleRecordResolverImpl final
                                     ExecutionContext* execution_context)
       : ContextLifecycleObserver(execution_context), modulator_(modulator) {}
 
-  void Trace(blink::Visitor*) override;
+  void Trace(Visitor*) override;
   USING_GARBAGE_COLLECTED_MIXIN(ModuleRecordResolverImpl);
 
  private:
@@ -38,7 +38,8 @@ class CORE_EXPORT ModuleRecordResolverImpl final
 
   void RegisterModuleScript(const ModuleScript*) final;
   void UnregisterModuleScript(const ModuleScript*) final;
-  const ModuleScript* GetHostDefined(const ModuleRecord&) const final;
+  const ModuleScript* GetModuleScriptFromModuleRecord(
+      const ModuleRecord&) const final;
 
   // Implements "Runtime Semantics: HostResolveImportedModule" per HTML spec.
   // https://html.spec.whatwg.org/C/#hostresolveimportedmodule(referencingscriptormodule,-specifier))
diff --git a/chromium/third_party/blink/renderer/core/script/module_record_resolver_impl_test.cc b/chromium/third_party/blink/renderer/core/script/module_record_resolver_impl_test.cc
index d369141fc7b..0b59125c96c 100644
--- a/chromium/third_party/blink/renderer/core/script/module_record_resolver_impl_test.cc
+++ b/chromium/third_party/blink/renderer/core/script/module_record_resolver_impl_test.cc
@@ -25,7 +25,7 @@ class ModuleRecordResolverImplTestModulator final : public DummyModulator {
   ModuleRecordResolverImplTestModulator() {}
   ~ModuleRecordResolverImplTestModulator() override {}
 
-  void Trace(blink::Visitor*) override;
+  void Trace(Visitor*) override;
 
   void SetScriptState(ScriptState* script_state) {
     script_state_ = script_state;
@@ -57,7 +57,7 @@ class ModuleRecordResolverImplTestModulator final : public DummyModulator {
   Member<ModuleScript> module_script_;
 };
 
-void ModuleRecordResolverImplTestModulator::Trace(blink::Visitor* visitor) {
+void ModuleRecordResolverImplTestModulator::Trace(Visitor* visitor) {
   visitor->Trace(script_state_);
   visitor->Trace(module_script_);
   DummyModulator::Trace(visitor);
diff --git a/chromium/third_party/blink/renderer/core/script/module_script.cc b/chromium/third_party/blink/renderer/core/script/module_script.cc
index 4879fe71667..16fbb40347e 100644
--- a/chromium/third_party/blink/renderer/core/script/module_script.cc
+++ b/chromium/third_party/blink/renderer/core/script/module_script.cc
@@ -6,6 +6,8 @@
 
 #include "third_party/blink/renderer/bindings/core/v8/script_value.h"
 #include "third_party/blink/renderer/core/script/module_record_resolver.h"
+#include "third_party/blink/renderer/core/workers/worker_global_scope.h"
+#include "third_party/blink/renderer/core/workers/worker_reporting_proxy.h"
 #include "third_party/blink/renderer/platform/bindings/script_state.h"
 #include "v8/include/v8.h"
 
@@ -90,7 +92,7 @@ KURL ModuleScript::ResolveModuleSpecifier(const String& module_request,
   return url;
 }
 
-void ModuleScript::Trace(blink::Visitor* visitor) {
+void ModuleScript::Trace(Visitor* visitor) {
   visitor->Trace(settings_object_);
   visitor->Trace(record_.UnsafeCast<v8::Value>());
   visitor->Trace(parse_error_);
@@ -104,6 +106,21 @@ void ModuleScript::RunScript(LocalFrame* frame, const SecurityOrigin*) {
                                   Modulator::CaptureEvalErrorFlag::kReport);
 }
 
+void ModuleScript::RunScriptOnWorker(WorkerGlobalScope& worker_global_scope) {
+  DCHECK(worker_global_scope.IsContextThread());
+
+  WorkerReportingProxy& worker_reporting_proxy =
+      worker_global_scope.ReportingProxy();
+
+  worker_reporting_proxy.WillEvaluateModuleScript();
+  // This |error| is always null because the second argument is |kReport|.
+  // TODO(nhiroki): Catch an error when an evaluation error happens.
+  // (https://crbug.com/680046)
+  ScriptValue error = SettingsObject()->ExecuteModule(
+      this, Modulator::CaptureEvalErrorFlag::kReport);
+  worker_reporting_proxy.DidEvaluateModuleScript(error.IsEmpty());
+}
+
 std::ostream& operator<<(std::ostream& stream,
                          const ModuleScript& module_script) {
   stream << "ModuleScript[" << &module_script;
diff --git a/chromium/third_party/blink/renderer/core/script/module_script.h b/chromium/third_party/blink/renderer/core/script/module_script.h
index 45e7fe86874..50d32f0ed33 100644
--- a/chromium/third_party/blink/renderer/core/script/module_script.h
+++ b/chromium/third_party/blink/renderer/core/script/module_script.h
@@ -48,7 +48,7 @@ class CORE_EXPORT ModuleScript : public Script {
   KURL ResolveModuleSpecifier(const String& module_request,
                               String* failure_reason = nullptr) const;
 
-  void Trace(blink::Visitor*) override;
+  void Trace(Visitor*) override;
 
   virtual void ProduceCache() {}
 
@@ -67,6 +67,7 @@ class CORE_EXPORT ModuleScript : public Script {
     return mojom::ScriptType::kModule;
   }
   void RunScript(LocalFrame*, const SecurityOrigin*) override;
+  void RunScriptOnWorker(WorkerGlobalScope&) override;
 
   friend class ModuleTreeLinkerTestModulator;
 
diff --git a/chromium/third_party/blink/renderer/core/script/module_script_test.cc b/chromium/third_party/blink/renderer/core/script/module_script_test.cc
index 204391421b7..6d1849c14f5 100644
--- a/chromium/third_party/blink/renderer/core/script/module_script_test.cc
+++ b/chromium/third_party/blink/renderer/core/script/module_script_test.cc
@@ -11,6 +11,7 @@
 #include "third_party/blink/renderer/bindings/core/v8/v8_binding_for_core.h"
 #include "third_party/blink/renderer/bindings/core/v8/v8_binding_for_testing.h"
 #include "third_party/blink/renderer/core/script/js_module_script.h"
+#include "third_party/blink/renderer/core/script/value_wrapper_synthetic_module_script.h"
 #include "third_party/blink/renderer/core/testing/dummy_modulator.h"
 #include "third_party/blink/renderer/core/testing/page_test_base.h"
 #include "third_party/blink/renderer/platform/loader/fetch/cached_metadata.h"
@@ -35,7 +36,7 @@ class ModuleScriptTestModulator final : public DummyModulator {
     return Vector<ModuleRequest>();
   }
 
-  void Trace(blink::Visitor* visitor) override {
+  void Trace(Visitor* visitor) override {
     visitor->Trace(script_state_);
     DummyModulator::Trace(visitor);
   }
@@ -82,6 +83,14 @@ class ModuleScriptTest : public ::testing::Test {
         ScriptFetchOptions());
   }
 
+  static ValueWrapperSyntheticModuleScript*
+  CreateValueWrapperSyntheticModuleScript(Modulator* modulator,
+                                          v8::Local<v8::Value> local_value) {
+    return ValueWrapperSyntheticModuleScript::CreateWithDefaultExport(
+        local_value, modulator, KURL("https://fox.url/script.js"),
+        KURL("https://fox.url/"), ScriptFetchOptions());
+  }
+
   // Tests |window.foo| is set correctly, and reset |window.foo| for the next
   // test.
   static void TestFoo(V8TestingScope& scope) {
@@ -239,4 +248,14 @@ TEST_F(ModuleScriptTest, V8CodeCache) {
       V8CodeCache::TagForCodeCache(cache_handler)));
 }
 
-}  // namespace blink
+TEST_F(ModuleScriptTest, ValueWrapperSyntheticModuleScript) {
+  V8TestingScope scope;
+  v8::Local<v8::Value> local_value(v8::Number::New(scope.GetIsolate(), 1234));
+  Modulator* modulator =
+      MakeGarbageCollected<ModuleScriptTestModulator>(scope.GetScriptState());
+  ValueWrapperSyntheticModuleScript* module_script =
+      CreateValueWrapperSyntheticModuleScript(modulator, local_value);
+  ASSERT_FALSE(module_script->Record().IsNull());
+}
+
+}  // namespace blink
\ No newline at end of file
diff --git a/chromium/third_party/blink/renderer/core/script/pending_script.cc b/chromium/third_party/blink/renderer/core/script/pending_script.cc
index b43e498c25a..b8fe2d8ab33 100644
--- a/chromium/third_party/blink/renderer/core/script/pending_script.cc
+++ b/chromium/third_party/blink/renderer/core/script/pending_script.cc
@@ -25,15 +25,15 @@
 
 #include "third_party/blink/renderer/core/script/pending_script.h"
 
-#include "third_party/blink/public/mojom/web_feature/web_feature.mojom-shared.h"
+#include "third_party/blink/public/mojom/web_feature/web_feature.mojom-blink.h"
 #include "third_party/blink/renderer/bindings/core/v8/script_controller.h"
 #include "third_party/blink/renderer/core/dom/document.h"
 #include "third_party/blink/renderer/core/dom/document_parser_timing.h"
 #include "third_party/blink/renderer/core/frame/csp/content_security_policy.h"
 #include "third_party/blink/renderer/core/frame/local_frame.h"
-#include "third_party/blink/renderer/core/frame/use_counter.h"
 #include "third_party/blink/renderer/core/script/ignore_destructive_write_count_incrementer.h"
 #include "third_party/blink/renderer/core/script/script_element_base.h"
+#include "third_party/blink/renderer/platform/instrumentation/use_counter.h"
 #include "third_party/blink/renderer/platform/scheduler/public/frame_scheduler.h"
 
 namespace blink {
@@ -72,7 +72,7 @@ void PendingScript::Dispose() {
   DCHECK(!IsWatchingForLoad());
 
   starting_position_ = TextPosition::BelowRangePosition();
-  parser_blocking_load_start_time_ = TimeTicks();
+  parser_blocking_load_start_time_ = base::TimeTicks();
 
   DisposeInternal();
   element_ = nullptr;
@@ -122,7 +122,7 @@ ScriptElementBase* PendingScript::GetElement() const {
 
 void PendingScript::MarkParserBlockingLoadStartTime() {
   DCHECK(parser_blocking_load_start_time_.is_null());
-  parser_blocking_load_start_time_ = CurrentTimeTicks();
+  parser_blocking_load_start_time_ = base::TimeTicks::Now();
 }
 
 // <specdef href="https://html.spec.whatwg.org/C/#execute-the-script-block">
@@ -172,7 +172,7 @@ void PendingScript::ExecuteScriptBlock(const KURL& document_url) {
   const bool was_canceled = WasCanceled();
   const bool is_external = IsExternal();
   const bool created_during_document_write = WasCreatedDuringDocumentWrite();
-  const TimeTicks parser_blocking_load_start_time =
+  const base::TimeTicks parser_blocking_load_start_time =
       ParserBlockingLoadStartTime();
   const bool is_controlled_by_script_runner = IsControlledByScriptRunner();
   ScriptElementBase* element = element_;
@@ -192,7 +192,7 @@ void PendingScript::ExecuteScriptBlockInternal(
     bool was_canceled,
     bool is_external,
     bool created_during_document_write,
-    TimeTicks parser_blocking_load_start_time,
+    base::TimeTicks parser_blocking_load_start_time,
     bool is_controlled_by_script_runner) {
   Document& element_document = element->GetDocument();
   Document* context_document = element_document.ContextDocument();
@@ -204,17 +204,17 @@ void PendingScript::ExecuteScriptBlockInternal(
     return;
   }
 
-  if (parser_blocking_load_start_time > TimeTicks()) {
+  if (parser_blocking_load_start_time > base::TimeTicks()) {
     DocumentParserTiming::From(element_document)
         .RecordParserBlockedOnScriptLoadDuration(
-            CurrentTimeTicks() - parser_blocking_load_start_time,
+            base::TimeTicks::Now() - parser_blocking_load_start_time,
             created_during_document_write);
   }
 
   if (was_canceled)
     return;
 
-  TimeTicks script_exec_start_time = CurrentTimeTicks();
+  base::TimeTicks script_exec_start_time = base::TimeTicks::Now();
 
   {
     if (element->ElementHasDuplicateAttributes()) {
@@ -235,48 +235,51 @@ void PendingScript::ExecuteScriptBlockInternal(
     IgnoreDestructiveWriteCountIncrementer incrementer(
         needs_increment ? context_document : nullptr);
 
-    // <spec step="4">Let old script element be the value to which the script
-    // element's node document's currentScript object was most recently
+    // <spec step="4.A.1">Let old script element be the value to which the
+    // script element's node document's currentScript object was most recently
     // set.</spec>
     //
     // This is implemented as push/popCurrentScript().
 
-    // <spec step="5">Switch on the script's type:</spec>
-    //
-    // <spec step="5.A">"classic"</spec>
+    // <spec step="4">Switch on the script's type:</spec>
+
+    // <spec step="4.A">"classic"</spec>
     //
-    // <spec step="5.A.1">If the script element's root is not a shadow root,
+    // <spec step="4.A.2">If the script element's root is not a shadow root,
     // then set the script element's node document's currentScript attribute to
     // the script element. Otherwise, set it to null.</spec>
     //
-    // <spec step="5.B">"module"</spec>
+    // Note: The shadow root check is implemented in
+    // HTMLScriptElement::SetScriptElementForBinding().
+
+    // <spec step="4.B">"module"</spec>
     //
-    // <spec step="5.B.1">Set the script element's node document's currentScript
-    // attribute to null.</spec>
+    // <spec step="4.B.1">Assert: The script element's node document's
+    // currentScript attribute is null.</spec>
     ScriptElementBase* current_script = nullptr;
     if (script->GetScriptType() == mojom::ScriptType::kClassic)
       current_script = element;
     context_document->PushCurrentScript(current_script);
 
-    // <spec step="5.A">"classic"</spec>
+    // <spec step="4.A">"classic"</spec>
     //
-    // <spec step="5.A.2">Run the classic script given by the script's
+    // <spec step="4.A.3">Run the classic script given by the script's
     // script.</spec>
     //
     // Note: This is where the script is compiled and actually executed.
     //
-    // <spec step="5.B">"module"</spec>
+    // <spec step="4.B">"module"</spec>
     //
-    // <spec step="5.B.2">Run the module script given by the script's
+    // <spec step="4.B.2">Run the module script given by the script's
     // script.</spec>
     script->RunScript(context_document->GetFrame(),
                       element_document.GetSecurityOrigin());
 
-    // <spec step="6">Set the script element's node document's currentScript
+    // <spec step="4.A.4">Set the script element's node document's currentScript
     // attribute to old script element.</spec>
     context_document->PopCurrentScript(current_script);
 
-    // <spec step="7">Decrement the ignore-destructive-writes counter of
+    // <spec step="5">Decrement the ignore-destructive-writes counter of
     // neutralized doc, if it was incremented in the earlier step.</spec>
     //
     // Implemented as the scope out of IgnoreDestructiveWriteCountIncrementer.
@@ -289,17 +292,17 @@ void PendingScript::ExecuteScriptBlockInternal(
   if (!is_controlled_by_script_runner) {
     DocumentParserTiming::From(element_document)
         .RecordParserBlockedOnScriptExecutionDuration(
-            CurrentTimeTicks() - script_exec_start_time,
+            base::TimeTicks::Now() - script_exec_start_time,
             created_during_document_write);
   }
 
-  // <spec step="8">If the script is from an external file, then fire an event
+  // <spec step="6">If the script is from an external file, then fire an event
   // named load at the script element.</spec>
   if (is_external)
     element->DispatchLoadEvent();
 }
 
-void PendingScript::Trace(blink::Visitor* visitor) {
+void PendingScript::Trace(Visitor* visitor) {
   visitor->Trace(element_);
   visitor->Trace(client_);
   visitor->Trace(original_context_document_);
@@ -315,6 +318,7 @@ bool PendingScript::IsControlledByScriptRunner() const {
     case ScriptSchedulingType::kParserBlocking:
     case ScriptSchedulingType::kParserBlockingInline:
     case ScriptSchedulingType::kImmediate:
+    case ScriptSchedulingType::kForceDefer:
       return false;
 
     case ScriptSchedulingType::kInOrder:
diff --git a/chromium/third_party/blink/renderer/core/script/pending_script.h b/chromium/third_party/blink/renderer/core/script/pending_script.h
index cfc8a018ca8..08b44d08616 100644
--- a/chromium/third_party/blink/renderer/core/script/pending_script.h
+++ b/chromium/third_party/blink/renderer/core/script/pending_script.h
@@ -53,7 +53,7 @@ class CORE_EXPORT PendingScriptClient : public GarbageCollectedMixin {
   // streaming finishes.
   virtual void PendingScriptFinished(PendingScript*) = 0;
 
-  void Trace(blink::Visitor* visitor) override {}
+  void Trace(Visitor* visitor) override {}
 };
 
 // A container for an script after "prepare a script" until it is executed.
@@ -73,7 +73,7 @@ class CORE_EXPORT PendingScript
   // Returns the time the load of this script started blocking the parser, or
   // zero if this script hasn't yet blocked the parser, in
   // monotonicallyIncreasingTime.
-  TimeTicks ParserBlockingLoadStartTime() const {
+  base::TimeTicks ParserBlockingLoadStartTime() const {
     return parser_blocking_load_start_time_;
   }
 
@@ -85,7 +85,7 @@ class CORE_EXPORT PendingScript
 
   virtual mojom::ScriptType GetScriptType() const = 0;
 
-  virtual void Trace(blink::Visitor*);
+  virtual void Trace(Visitor*);
   const char* NameInHeapSnapshot() const override { return "PendingScript"; }
 
   // Returns nullptr when "script's script is null", i.e. an error occurred.
@@ -153,7 +153,7 @@ class CORE_EXPORT PendingScript
       bool was_canceled,
       bool is_external,
       bool created_during_document_write,
-      TimeTicks parser_blocking_load_start_time,
+      base::TimeTicks parser_blocking_load_start_time,
       bool is_controlled_by_script_runner);
 
   // |m_element| must points to the corresponding ScriptLoader's
@@ -162,7 +162,7 @@ class CORE_EXPORT PendingScript
   Member<ScriptElementBase> element_;
 
   TextPosition starting_position_;  // Only used for inline script tags.
-  TimeTicks parser_blocking_load_start_time_;
+  base::TimeTicks parser_blocking_load_start_time_;
 
   ScriptSchedulingType scheduling_type_ = ScriptSchedulingType::kNotSet;
 
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/PRESUBMIT.py b/chromium/third_party/blink/renderer/core/script/resources/layered_api/PRESUBMIT.py
new file mode 100644
index 00000000000..4364aafa726
--- /dev/null
+++ b/chromium/third_party/blink/renderer/core/script/resources/layered_api/PRESUBMIT.py
@@ -0,0 +1,39 @@
+# Copyright 2019 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+
+import sys
+
+
+def _CommonChecks(input_api, output_api):
+  results = []
+  # TODO(tkent): {kv-storage,toast,virtual-scroller}/.eslintrc.js specify babel-eslint parser, which
+  # is not in third_party/node/node_modules/.
+  mjs_files = input_api.AffectedFiles(
+      file_filter=lambda f: (f.LocalPath().endswith('.mjs') and
+                             not '/virtual-scroller/' in f.LocalPath() and
+                             not '/kv-storage/' in f.LocalPath() and
+                             not '/toast/' in f.LocalPath()),
+      include_deletes=False)
+  if not mjs_files:
+    return results
+  try:
+    old_sys_path = sys.path[:]
+    cwd = input_api.PresubmitLocalPath()
+    sys.path += [input_api.os_path.join(cwd, '..', '..', '..', '..', '..',
+                                        '..', '..', 'tools')]
+    import web_dev_style.js_checker
+    checker = web_dev_style.js_checker.JSChecker(input_api, output_api)
+    results += checker.RunEsLintChecks(mjs_files)
+  finally:
+    sys.path = old_sys_path
+  return results
+
+
+def CheckChangeOnUpload(input_api, output_api):
+  return _CommonChecks(input_api, output_api)
+
+
+def CheckChangeOnCommit(input_api, output_api):
+  return _CommonChecks(input_api, output_api)
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/README.md b/chromium/third_party/blink/renderer/core/script/resources/layered_api/README.md
index 270d8117aa5..479818efa35 100644
--- a/chromium/third_party/blink/renderer/core/script/resources/layered_api/README.md
+++ b/chromium/third_party/blink/renderer/core/script/resources/layered_api/README.md
@@ -22,11 +22,27 @@ and commit these files together with the changes under resources/layered_api/.
 
 ## Which files are bundled
 
-All files under this directory will be included in the grdp and thus bundled
-in the Chromium binary, except for
+All files under
 
-- Files directly under `core/script/resources/layered_api`, or
-- Files starting with '.', 'README', or 'OWNERS'.
+- Sub-directories which have 'index.mjs' or
+- Directories of which last path component is 'internal'
+
+will be included in the grdp and thus bundled in the Chrome binary,
+except for files starting with '.', 'README', or 'OWNERS'.
 
 So be careful about binary size increase when you add new files or add more
 contents to existing files.
+
+## What are exposed
+
+All bundled resources are mapped to `std-internal://path-relative-to-here`, and
+`std-internal:` resources are not accessible from the web.  Resources loaded as
+`std-internal:` can import other `std-internal:` resources.
+
+For example, `layered_api/foo/bar/baz.mjs` is mapped to
+`std-internal://foo/bar/baz.mjs`.
+
+All `index.mjs` resources are mapped to `std:directory-name-relative-to-here`
+too, and they are web-exposed.  For example,
+`layered_api/elements/toast/index.mjs` is mapped to `std:elements/toast` as
+well as `std-internal://elements/toast/index.mjs`.
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/internal/reflection.mjs b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/internal/reflection.mjs
new file mode 100644
index 00000000000..989a4aa1ff1
--- /dev/null
+++ b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/internal/reflection.mjs
@@ -0,0 +1,63 @@
+// Copyright 2019 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/**
+ * @file Manage attribute-property reflections.
+ *     https://html.spec.whatwg.org/C/common-dom-interfaces.html#reflecting-content-attributes-in-idl-attributes
+ */
+
+/**
+ * Add a bool reflection property to the specified prototype for the specified
+ * attribute.
+ *
+ * @param {!Object} proto An element prototype
+ * @param {string} attrName An attribute name
+ * @param {string} propName An optional property name. attrName will be used if
+ *     this argument is omitted.
+ */
+export function installBool(proto, attrName, propName = attrName) {
+  let getter = function() {
+    return this.hasAttribute(attrName);
+  };
+  let setter = function(value) {
+    this.toggleAttribute(attrName, Boolean(value));
+  };
+  Object.defineProperty(
+      getter, 'name',
+      {configurable: true, enumerable: false, value: 'get ' + propName});
+  Object.defineProperty(
+      setter, 'name',
+      {configurable: true, enumerable: false, value: 'set ' + propName});
+  Object.defineProperty(
+      proto, propName,
+      {configurable: true, enumerable: true, get: getter, set: setter});
+}
+
+/**
+ * Add a DOMString reflection property to the specified prototype for the
+ * specified attribute.
+ *
+ * @param {!Element} element An element prototype
+ * @param {string} attrName An attribute name
+ * @param {string} propName An optional property name. attrName will be used if
+ *     this argument is omitted.
+ */
+export function installString(proto, attrName, propName = attrName) {
+  let getter = function() {
+    let value = this.getAttribute(attrName);
+    return value === null ? '' : value;
+  };
+  let setter = function(value) {
+    this.setAttribute(attrName, value);
+  };
+  Object.defineProperty(
+      getter, 'name',
+      {configurable: true, enumerable: false, value: 'get ' + propName});
+  Object.defineProperty(
+      setter, 'name',
+      {configurable: true, enumerable: false, value: 'set ' + propName});
+  Object.defineProperty(
+      proto, propName,
+      {configurable: true, enumerable: true, get: getter, set: setter});
+}
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/switch/README.md b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/switch/README.md
new file mode 100644
index 00000000000..c8962f767cb
--- /dev/null
+++ b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/switch/README.md
@@ -0,0 +1,3 @@
+# Switch control element
+
+https://github.com/tkent-google/std-switch/blob/master/README.md
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/switch/face_utils.mjs b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/switch/face_utils.mjs
new file mode 100644
index 00000000000..8db1f4177ff
--- /dev/null
+++ b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/switch/face_utils.mjs
@@ -0,0 +1,75 @@
+// Copyright 2019 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/**
+ * @file Utilities for form-associated custom elements
+ */
+
+import * as reflection from '../internal/reflection.mjs';
+
+function installGetter(proto, propName, getter) {
+  Object.defineProperty(
+      getter, 'name',
+      {configurable: true, enumerable: false, value: 'get ' + propName});
+  Object.defineProperty(
+      proto, propName, {configurable: true, enumerable: true, get: getter});
+}
+
+/**
+ * Add the following properties to |proto|.
+ *   - disabled
+ *   - name
+ *   - type
+ *   - form
+ *   - willValidate
+ *   - validity
+ *   - validationMessage
+ *   - labels
+ *   - checkValidity()
+ *   - reportValidity()
+ *   - setCustomValidity(error)
+ *
+ * @param {!Object} proto An Element prototype which will have properties
+ * @param {!Symbol} internals A Symbol of the ElementInternals property of the
+ *     element
+ */
+export function installPropertiesAndFunctions(proto, internals) {
+  reflection.installBool(proto, 'disabled');
+  reflection.installString(proto, 'name');
+  installGetter(proto, 'type', function() {
+    if (!(this instanceof proto.constructor)) {
+      throw TypeError(
+          'The context object is not an instance of ' + proto.contructor.name);
+    }
+    return this.localName;
+  });
+
+  installGetter(proto, 'form', function() {
+    return this[internals].form;
+  });
+  installGetter(proto, 'willValidate', function() {
+    return this[internals].willValidate;
+  });
+  installGetter(proto, 'validity', function() {
+    return this[internals].validity;
+  });
+  installGetter(proto, 'validationMessage', function() {
+    return this[internals].validationMessage;
+  });
+  installGetter(proto, 'labels', function() {
+    return this[internals].labels;
+  });
+  proto.checkValidity = function() {
+    return this[internals].checkValidity();
+  };
+  proto.reportValidity = function() {
+    return this[internals].reportValidity();
+  };
+  proto.setCustomValidity = function(error) {
+    if (error === undefined) {
+      throw new TypeError('Too few arguments');
+    }
+    this[internals].setValidity({customError: true}, error);
+  };
+}
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/switch/index.mjs b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/switch/index.mjs
new file mode 100644
index 00000000000..6c7be3d46fc
--- /dev/null
+++ b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/switch/index.mjs
@@ -0,0 +1,128 @@
+// Copyright 2019 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import * as face from './face_utils.mjs';
+import * as reflection from '../internal/reflection.mjs';
+import { SwitchTrack } from './track.mjs';
+import * as style from './style.mjs';
+
+// https://github.com/tkent-google/std-switch/issues/2
+const STATE_ATTR = 'on';
+
+// Private property symbols
+// TODO(tkent): Use private fields.
+const _internals = Symbol();
+const _track = Symbol();
+const _rippleElement = Symbol();
+const _containerElement = Symbol();
+
+export class StdSwitchElement extends HTMLElement {
+  // TODO(tkent): The following should be |static fooBar = value;|
+  // after enabling babel-eslint.
+  static get formAssociated() {
+    return true;
+  }
+  static get observedAttributes() {
+    return [STATE_ATTR];
+  }
+
+  constructor() {
+    super();
+    if (new.target !== StdSwitchElement) {
+      throw new TypeError('Illegal constructor: StdSwitchElement is not ' +
+                          'extensible for now');
+    }
+    this[_internals] = this.attachInternals();
+    this._initializeDOM();
+
+    this.addEventListener('click', this._onClick);
+    this.addEventListener('keypress', this._onKeyPress);
+  }
+
+  attributeChangedCallback(attrName, oldValue, newValue) {
+    if (attrName == STATE_ATTR) {
+      this[_track].value = newValue !== null;
+      // TODO(tkent): We should not add aria-checked attribute.
+      // https://github.com/WICG/aom/issues/127
+      this.setAttribute('aria-checked', newValue !== null ? 'true' : 'false');
+    }
+  }
+
+  connectedCallback() {
+    // TODO(tkent): We should not add tabindex attribute.
+    // https://github.com/w3c/webcomponents/issues/762
+    if (!this.hasAttribute('tabindex')) {
+      this.setAttribute('tabindex', '0');
+    }
+
+    // TODO(tkent): We should not add role attribute.
+    // https://github.com/WICG/aom/issues/127
+    if (!this.hasAttribute('role')) {
+      this.setAttribute('role', 'switch');
+    }
+  }
+
+  // TODO(tkent): Make this private.
+  _initializeDOM() {
+    let factory = this.ownerDocument;
+    let root = this.attachShadow({mode: 'closed'});
+    this[_containerElement] = factory.createElement('span');
+    this[_containerElement].id = 'container';
+    // Shadow elements should be invisible for a11y technologies.
+    this[_containerElement].setAttribute('aria-hidden', 'true');
+    root.appendChild(this[_containerElement]);
+
+    this[_track] = new SwitchTrack(factory);
+    this[_containerElement].appendChild(this[_track].element);
+    this[_track].value = this.on;
+
+    let thumbElement = this[_containerElement].appendChild(factory.createElement('span'));
+    thumbElement.id = 'thumb';
+    thumbElement.part.add('thumb');
+
+    this[_rippleElement] = thumbElement.appendChild(factory.createElement('span'));
+    this[_rippleElement].id = 'ripple';
+
+    root.adoptedStyleSheets = [style.styleSheetFactory()()];
+  }
+
+  // TODO(tkent): Make this private.
+  _onClick(event) {
+    for (let element of this[_containerElement].querySelectorAll('*')) {
+      style.markTransition(element);
+    }
+    this.on = !this.on;
+    this.dispatchEvent(new Event('input', {bubbles: true}));
+    this.dispatchEvent(new Event('change', {bubbles: true}));
+  }
+
+  // TODO(tkent): Make this private.
+  _onKeyPress(event) {
+    if (event.code == 'Space') {
+      // Do not scroll the page.
+      event.preventDefault();
+      this._onClick(event);
+    }
+  }
+}
+
+reflection.installBool(StdSwitchElement.prototype, STATE_ATTR);
+reflection.installBool(
+    StdSwitchElement.prototype, 'default' + STATE_ATTR,
+    'default' + STATE_ATTR.charAt(0).toUpperCase() + STATE_ATTR.substring(1));
+face.installPropertiesAndFunctions(StdSwitchElement.prototype, _internals);
+
+// This is necessary for anyObject.toString.call(switchInstance).
+Object.defineProperty(StdSwitchElement.prototype, Symbol.toStringTag, {
+  configurable: true,
+  enumerable: false,
+  value: 'StdSwitchElement',
+  writable: false
+});
+
+customElements.define('std-switch', StdSwitchElement);
+delete StdSwitchElement.formAssociated;
+delete StdSwitchElement.observedAttributes;
+delete StdSwitchElement.prototype.attributeChangedCallback;
+delete StdSwitchElement.prototype.connectedCallback;
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/switch/style.mjs b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/switch/style.mjs
new file mode 100644
index 00000000000..6b0bc2eca78
--- /dev/null
+++ b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/switch/style.mjs
@@ -0,0 +1,224 @@
+// Copyright 2019 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Style constant values.
+const COLOR_ON = '#0077FF';
+const TRACK_RADIUS = '13px';
+const TRACK_BORDER_WIDTH = '2px';
+const THUMB_HEIGHT = '22px';
+const THUMB_WIDTH = '22px';
+const THUMB_MARGIN_START = '2px';
+const THUMB_MARGIN_END = '2px';
+
+// Returns a function returning a CSSStyleSheet().
+// TODO(tkent): Share this stylesheet factory feature with elements/toast/.
+export function styleSheetFactory() {
+  let styleSheet;
+  return () => {
+    if (!styleSheet) {
+      styleSheet = new CSSStyleSheet();
+      styleSheet.replaceSync(`
+:host {
+  block-size: 26px;
+  border: none;
+  box-sizing: border-box;
+  display: inline-block;
+  inline-size: 54px;
+  user-select: none;
+  vertical-align: middle;
+}
+
+#container {
+  align-items: center;
+  block-size: 100%;
+  display: inline-flex;
+  inline-size: 100%;
+}
+
+#thumb {
+  background: white;
+  block-size: ${THUMB_HEIGHT};
+  border-radius: calc(${THUMB_HEIGHT} / 2);
+  border: 1px solid black;
+  box-sizing: border-box;
+  display: inline-block;
+  margin-inline-start: calc(-100% + ${THUMB_MARGIN_START});
+  inline-size: ${THUMB_WIDTH};
+}
+
+/* :host::part(thumb-transitioning) doesn't work. crbug.com/980506 */
+#thumb[part~="thumb-transitioning"] {
+  transition: all linear 0.1s;
+}
+
+:host([on]) #thumb {
+  border: 1px solid ${COLOR_ON};
+  margin-inline-start: calc(0px - ${THUMB_WIDTH} - ${THUMB_MARGIN_END});
+}
+
+#track {
+  block-size: 100%;
+  border-radius: ${TRACK_RADIUS};
+  border: ${TRACK_BORDER_WIDTH} solid #dddddd;
+  box-shadow: 0 0 0 1px #f8f8f8;
+  box-sizing: border-box;
+  display: inline-block;
+  inline-size: 100%;
+  overflow: hidden;
+  padding: 0px;
+}
+
+#trackFill {
+  background: ${COLOR_ON};
+  block-size: 100%;
+  border-radius: calc(${TRACK_RADIUS}) - ${TRACK_BORDER_WIDTH});
+  box-shadow: none;
+  box-sizing: border-box;
+  display: inline-block;
+  inline-size: 0%;
+  vertical-align: top;
+}
+
+#trackFill[part~="track-fill-transitioning"] {
+  transition: all linear 0.1s;
+}
+
+:host([on]) #track {
+  border: ${TRACK_BORDER_WIDTH} solid ${COLOR_ON};
+}
+
+:host(:focus) {
+  outline-offset: 4px;
+}
+
+:host(:focus) #track {
+  box-shadow: 0 0 0 2px #f8f8f8;
+}
+
+:host([on]:focus) #track {
+  box-shadow: 0 0 0 2px #dddddd;
+}
+
+:host(:focus) #thumb {
+  border: 2px solid black;
+}
+
+:host([on]:focus) #thumb {
+  border: 2px solid ${COLOR_ON};
+}
+
+:host(:not(:focus-visible):focus) {
+  outline: none;
+}
+
+:host(:not(:disabled):hover) #thumb {
+  inline-size: 26px;
+}
+
+:host([on]:not(:disabled):hover) #thumb {
+  margin-inline-start: calc(0px - 26px - ${THUMB_MARGIN_END});
+}
+
+:host(:active) #track {
+  background: #dddddd;
+}
+
+:host([on]:active) #track {
+  border: 2px solid #77bbff;
+  box-shadow: 0 0 0 2px #f8f8f8;
+}
+
+:host([on]:active) #trackFill {
+  background: #77bbff;
+}
+
+:host(:disabled) {
+  opacity: 0.38;
+}
+
+/*
+ * display:inline-block in the :host ruleset overrides 'hidden' handling
+ * by the user agent.
+ */
+:host([hidden]) {
+  display: none;
+}
+
+`);
+    }
+    return styleSheet;
+  };
+}
+
+/**
+ * @param {!Element} element
+ */
+function setupTransitionCounter(element) {
+  if (element.runningTransitions !== undefined) {
+    return;
+  }
+  element.runningTransitions = 0;
+  element.addEventListener('transitionrun', e => {
+    if (e.target === element) {
+      ++element.runningTransitions;
+    }
+  });
+  let handleEndOrCancel = e => {
+    // Need to check runningTransitions>0 due to superfluous transitioncancel
+    // events; crbug.com/979556.
+    if (e.target === element && element.runningTransitions > 0) {
+      --element.runningTransitions;
+    }
+  };
+  element.addEventListener('transitionend', handleEndOrCancel);
+  element.addEventListener('transitioncancel', handleEndOrCancel);
+}
+
+/**
+ * Add '$part-transitioning' part to the element, and remove it on 'transitionend'
+ * event or remove it immediately if the element has no transitions.
+ *
+ * TODO(tkent): We should apply custom state.
+ *
+ * @param {!Element} element
+ */
+export function markTransition(element) {
+  // Should check hasAttribute() to avoid creating a DOMTokenList instance.
+  if (!element.hasAttribute('part') || element.part.length < 1) {
+    return;
+  }
+
+  setupTransitionCounter(element);
+
+  const partName = element.part[0] + '-transitioning';
+  if (element.part.contains(partName)) {
+    return;
+  }
+  // The style with partName might have transitions, and might have no
+  // transitions. We need to add partName anyway because we have no other
+  // ways to check existence of transitions.  Then, we need to remove
+  // partName because state change without markTransition() should have
+  // style without partName.
+  //
+  // We add partName in an animation frame, and continue to request
+  // animation frames until runningTransitions becomes 0. If the style with
+  // partName has no transitions, runningTransitions keeps 0, and the second
+  // animation frame removes partName.
+  window.requestAnimationFrame(() => {
+    element.part.add(partName);
+
+    // If the element has a transition, it must start on the rendering just
+    // after this rAF callback. So we check runningTransitions in the next
+    // frame.
+    const removeIfNoTransitions = () => {
+      // No transitions started, or all transitions were completed.
+      if (element.runningTransitions === 0) {
+        element.part.remove(partName);
+      } else {
+        window.requestAnimationFrame(removeIfNoTransitions);
+      }
+    };
+    window.requestAnimationFrame(removeIfNoTransitions);
+  });
+}
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/switch/track.mjs b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/switch/track.mjs
new file mode 100644
index 00000000000..aa8fc00c3d1
--- /dev/null
+++ b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/switch/track.mjs
@@ -0,0 +1,74 @@
+// Copyright 2019 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Private property symbols
+// TODO(tkent): Use private fields.
+const _value = Symbol();
+const _trackElement = Symbol();
+const _fillElement = Symbol();
+const _slotElement = Symbol();
+
+export class SwitchTrack {
+
+  /**
+   * @param {!Document} factory A factory for elements created for this track.
+   */
+  constructor(factory) {
+    this[_value] = false;
+    this._initializeDOM(factory);
+  }
+
+  /**
+   * @return {!Element}
+   */
+  get element() {
+    return this[_trackElement];
+  }
+
+  /**
+   * @param {Boolean} newValue
+   */
+  set value(newValue) {
+    let oldValue = this[_value];
+    this[_value] = Boolean(newValue);
+
+    let bar = this[_fillElement];
+    if (bar) {
+      bar.style.inlineSize = this[_value] ? '100%' : '0%';
+      if (oldValue != this[_value]) {
+        this._addSlot();
+      }
+    }
+  }
+
+  // TODO(tkent): Use private fields. #initializeDOM = factory => { ...};
+  /**
+   * @param {!Document} factory A factory for elements created for this track.
+   */
+  _initializeDOM(factory) {
+    this[_trackElement] = factory.createElement('div');
+    this[_trackElement].id = 'track';
+    this[_trackElement].part.add('track');
+    this[_fillElement] = factory.createElement('span');
+    this[_fillElement].id = 'trackFill';
+    this[_fillElement].part.add('track-fill');
+    this[_trackElement].appendChild(this[_fillElement]);
+    this[_slotElement] = factory.createElement('slot');
+    this._addSlot();
+  }
+
+  /**
+   * Add the <slot>
+   *   - next to _fillElement if _value is true
+   *   - as a child of _fillElement if _value is false
+   * This behavior is helpful to show text in the track.
+   */
+  _addSlot() {
+    if (this[_value]) {
+      this[_fillElement].appendChild(this[_slotElement]);
+    } else {
+      this[_trackElement].appendChild(this[_slotElement]);
+    }
+  }
+}
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/toast/.eslintrc.js b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/toast/.eslintrc.js
new file mode 100644
index 00000000000..8f9a67630c4
--- /dev/null
+++ b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/toast/.eslintrc.js
@@ -0,0 +1,338 @@
+// Copyright 2019 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+module.exports = {
+  root: true,
+  env: {
+    es6: true,
+    browser: true
+  },
+  'parser': 'babel-eslint',
+  parserOptions: {
+    sourceType: 'module',
+    ecmaVersion: 2019
+  },
+  rules: {
+    'for-direction': 'error',
+    'getter-return': 'error',
+    'no-async-promise-executor': 'error',
+    'no-await-in-loop': 'error',
+    'no-compare-neg-zero': 'error',
+    'no-cond-assign': ['error', 'except-parens'],
+    'no-console': 'error',
+    'no-constant-condition': ['error', {checkLoops: false}],
+    'no-control-regex': 'error',
+    'no-debugger': 'error',
+    'no-dupe-args': 'error',
+    'no-dupe-keys': 'error',
+    'no-duplicate-case': 'error',
+    'no-empty': 'error',
+    'no-empty-character-class': 'error',
+    'no-ex-assign': 'error',
+    'no-extra-boolean-cast': 'error',
+    'no-extra-parens': [
+      'error',
+      'all',
+      {
+        conditionalAssign: false,
+        nestedBinaryExpressions: false,
+        returnAssign: false
+      }
+    ],
+    'no-extra-semi': 'error',
+    'no-func-assign': 'error',
+    'no-inner-declarations': 'off',
+    'no-invalid-regexp': 'error',
+    'no-irregular-whitespace': 'error',
+    'no-misleading-character-class': 'error',
+    'no-obj-calls': 'error',
+    'no-prototype-builtins': 'error',
+    'no-regex-spaces': 'error',
+    'no-sparse-arrays': 'error',
+    'no-template-curly-in-string': 'error',
+    'no-unexpected-multiline': 'error',
+    'no-unreachable': 'error',
+    'no-unsafe-finally': 'off',
+    'no-unsafe-negation': 'error',
+    'use-isnan': 'error',
+    'valid-typeof': 'error',
+    'accessor-pairs': 'error',
+    'array-callback-return': 'error',
+    'block-scoped-var': 'off',
+    'class-methods-use-this': 'off',
+    'complexity': 'off',
+    'consistent-return': 'error',
+    'curly': ['error', 'all'],
+    'default-case': 'off',
+    'dot-location': ['error', 'property'],
+    'dot-notation': 'error',
+    'eqeqeq': 'error',
+    'guard-for-in': 'off',
+    'no-alert': 'error',
+    'no-caller': 'error',
+    'no-case-declarations': 'error',
+    'no-div-regex': 'off',
+    'no-else-return': 'error',
+    'no-empty-function': 'off',
+    'no-empty-pattern': 'error',
+    'no-eq-null': 'error',
+    'no-eval': 'error',
+    'no-extend-native': 'error',
+    'no-extra-bind': 'error',
+    'no-extra-label': 'error',
+    'no-fallthrough': 'error',
+    'no-floating-decimal': 'error',
+    'no-global-assign': 'error',
+    'no-implicit-coercion': 'error',
+    'no-implicit-globals': 'error',
+    'no-implied-eval': 'error',
+    'no-invalid-this': 'error',
+    'no-iterator': 'error',
+    'no-labels': ['error', {allowLoop: true}],
+    'no-lone-blocks': 'error',
+    'no-loop-func': 'error',
+    'no-magic-numbers': ['error', {ignore: [0, 1]}],
+    'no-multi-spaces': ['error', {ignoreEOLComments: true}],
+    'no-multi-str': 'error',
+    'no-new': 'error',
+    'no-new-func': 'error',
+    'no-new-wrappers': 'error',
+    'no-octal': 'error',
+    'no-octal-escape': 'error',
+    'no-param-reassign': 'off',
+    'no-process-env': 'error',
+    'no-proto': 'error',
+    'no-redeclare': 'error',
+    'no-restricted-properties': 'off',
+    'no-return-assign': ['error', 'except-parens'],
+    'no-return-await': 'error',
+    'no-script-url': 'off',
+    'no-self-assign': 'error',
+    'no-self-compare': 'error',
+    'no-sequences': 'error',
+    'no-throw-literal': 'error',
+    'no-unmodified-loop-condition': 'error',
+    'no-unused-expressions': 'error',
+    'no-unused-labels': 'error',
+    'no-useless-call': 'error',
+    'no-useless-concat': 'error',
+    'no-useless-escape': 'error',
+    'no-useless-return': 'error',
+    'no-void': 'error',
+    'no-warning-comments': 'off',
+    'no-with': 'error',
+    'prefer-promise-reject-errors': 'error',
+    'radix': ['error', 'as-needed'],
+    'require-await': 'off',
+    'vars-on-top': 'off',
+    'wrap-iife': ['error', 'outside'],
+    'yoda': ['error', 'never'],
+    'strict': ['error', 'global'],
+    'init-declarations': 'off',
+    'no-delete-var': 'error',
+    'no-label-var': 'error',
+    'no-restricted-globals': 'off',
+    'no-shadow': 'error',
+    'no-shadow-restricted-names': 'error',
+    'no-undef': 'error',
+    'no-undef-init': 'error',
+    'no-undefined': 'off',
+    'no-unused-vars': 'error',
+    'no-use-before-define': ['error', 'nofunc'],
+    'callback-return': 'off',
+    'global-require': 'error',
+    'handle-callback-err': 'error',
+    'no-buffer-constructor': 'error',
+    'no-mixed-requires': ['error', true],
+    'no-new-require': 'error',
+    'no-path-concat': 'error',
+    'no-process-exit': 'error',
+    'no-restricted-modules': 'off',
+    'no-sync': 'off',
+    'array-bracket-newline': ['error', {multiline: true}],
+    'array-bracket-spacing': ['error', 'never'],
+    'array-element-newline': 'off',
+    'block-spacing': ['error', 'always'],
+    'brace-style': [
+      'error',
+      '1tbs',
+      {allowSingleLine: false}
+    ],
+    camelcase: ['error', {properties: 'always'}],
+    'capitalized-comments': 'off',
+    'comma-dangle': ['error', 'always-multiline'],
+    'comma-spacing': [
+      'error',
+      {
+        before: false,
+        after: true
+      }
+    ],
+    'comma-style': ['error', 'last'],
+    'computed-property-spacing': ['error', 'never'],
+    'consistent-this': 'off',
+    'eol-last': 'error',
+    'func-call-spacing': ['error', 'never'],
+    'func-name-matching': 'error',
+    'func-names': 'off',
+    'func-style': ['error', 'declaration'],
+    'function-paren-newline': 'off',
+    'id-blacklist': 'off',
+    'id-length': 'off',
+    'id-match': 'off',
+    indent: 'off', // not really compatible with clang-format
+    'jsx-quotes': 'off',
+    'key-spacing': [
+      'error',
+      {
+        beforeColon: false,
+        afterColon: true,
+        mode: 'strict'
+      }
+    ],
+    'keyword-spacing': [
+      'error',
+      {
+        before: true,
+        after: true
+      }
+    ],
+    'line-comment-position': 'off',
+    'linebreak-style': ['error', 'unix'],
+    'lines-around-comment': 'off',
+    'max-depth': 'off',
+    'max-len': 'off',
+    'max-lines': 'off',
+    'max-nested-callbacks': 'off',
+    'max-params': 'off',
+    'max-statements': 'off',
+    'max-statements-per-line': ['error', {max: 1}],
+    'multiline-ternary': ['error', 'always-multiline'],
+    'new-cap': 'error',
+    'new-parens': 'error',
+    'newline-per-chained-call': 'off',
+    'no-array-constructor': 'error',
+    'no-bitwise': 'off',
+    'no-continue': 'off',
+    'no-inline-comments': 'off',
+    'no-lonely-if': 'error',
+    'no-mixed-operators': [
+      'error',
+      {
+        groups: [
+          ['&', '|', '^', '~', '<<', '>>', '>>>'],
+          ['==', '!=', '===', '!==', '>', '>=', '<', '<='],
+          ['&&', '||'],
+          ['in', 'instanceof']
+        ]
+      }
+    ],
+    'no-mixed-spaces-and-tabs': 'error',
+    'no-multi-assign': 'off',
+    'no-multiple-empty-lines': 'error',
+    'no-negated-condition': 'off',
+    'no-nested-ternary': 'error',
+    'no-new-object': 'error',
+    'no-plusplus': 'off',
+    'no-restricted-syntax': 'off',
+    'no-tabs': 'error',
+    'no-ternary': 'off',
+    'no-trailing-spaces': 'error',
+    'no-underscore-dangle': 'off',
+    'no-unneeded-ternary': 'error',
+    'no-whitespace-before-property': 'error',
+    'nonblock-statement-body-position': 'error',
+    'object-curly-newline': ['error', {consistent: true}],
+    'object-curly-spacing': ['error', 'never'],
+    'object-property-newline': 'off',
+    'one-var': ['error', 'never'],
+    'one-var-declaration-per-line': ['error', 'initializations'],
+    'operator-assignment': ['error', 'always'],
+    'operator-linebreak': ['error', 'after'],
+    'padded-blocks': ['error', 'never'],
+    'padding-line-between-statements': 'off',
+    'quote-props': ['error', 'as-needed'],
+    quotes: [
+      'error',
+      'single',
+      {
+        avoidEscape: true,
+        allowTemplateLiterals: true
+      }
+    ],
+    semi: ['error', 'always'],
+    'semi-spacing': 'error',
+    'semi-style': 'error',
+    'sort-keys': 'off',
+    'sort-vars': 'off',
+    'space-before-blocks': ['error', 'always'],
+    'space-before-function-paren': [
+      'error',
+      {
+        anonymous: 'always',
+        named: 'never'
+      }
+    ],
+    'space-in-parens': ['error', 'never'],
+    'space-infix-ops': 'error',
+    'space-unary-ops': [
+      'error',
+      {
+        words: true,
+        nonwords: false
+      }
+    ],
+    'spaced-comment': ['error', 'always'],
+    'switch-colon-spacing': 'error',
+    'template-tag-spacing': 'error',
+    'unicode-bom': 'error',
+    'wrap-regex': 'off',
+    'arrow-body-style': 'off',
+    'arrow-parens': ['error', 'as-needed'],
+    'arrow-spacing': 'error',
+    'constructor-super': 'error',
+    'generator-star-spacing': ['error', 'neither'],
+    'no-class-assign': 'error',
+    'no-confusing-arrow': 'off',
+    'no-const-assign': 'error',
+    'no-dupe-class-members': 'error',
+    'no-duplicate-imports': 'error',
+    'no-new-symbol': 'error',
+    'no-restricted-imports': 'off',
+    'no-this-before-super': 'error',
+    'no-useless-computed-key': 'error',
+    'no-useless-constructor': 'error',
+    'no-useless-rename': 'error',
+    'no-var': 'error',
+    'object-shorthand': 'error',
+    'prefer-arrow-callback': 'error',
+    'prefer-const': ['error', {ignoreReadBeforeAssign: true}],
+    'prefer-destructuring': [
+      'error',
+      {
+        VariableDeclarator: {
+          array: false,
+          object: true
+        },
+        AssignmentExpression: {
+          array: false,
+          object: false
+        }
+      },
+      {
+        enforceForRenamedProperties: false
+      }
+    ],
+    'prefer-numeric-literals': 'error',
+    'prefer-rest-params': 'error',
+    'prefer-spread': 'error',
+    'prefer-template': 'off',
+    'require-yield': 'error',
+    'rest-spread-spacing': 'error',
+    'sort-imports': 'off',
+    'symbol-description': 'error',
+    'template-curly-spacing': ['error', 'never'],
+    'yield-star-spacing': ['error', 'after']
+  }
+};
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/toast/OWNERS b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/toast/OWNERS
new file mode 100644
index 00000000000..d76cdfa11f0
--- /dev/null
+++ b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/toast/OWNERS
@@ -0,0 +1 @@
+fergal@chromium.org
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/toast/index.mjs b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/toast/index.mjs
new file mode 100644
index 00000000000..69232f8475a
--- /dev/null
+++ b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/toast/index.mjs
@@ -0,0 +1,280 @@
+/**
+ * Copyright 2019 The Chromium Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ *
+ * @fileoverview This file defines the class for the Standard Toast LAPI
+ * and the accompanying showToast() function.
+ * EXPLAINER: https://github.com/jackbsteinberg/std-toast
+ * TEST PATH: /chromium/src/third_party/blink/web_tests/external/wpt/std-toast/*
+ * @package
+ */
+
+import * as reflection from '../internal/reflection.mjs';
+
+const DEFAULT_DURATION = 3000;
+const TYPES = new Set(['success', 'warning', 'error']);
+
+function stylesheetFactory() {
+  let stylesheet;
+  return function generate() {
+    if (!stylesheet) {
+      stylesheet = new CSSStyleSheet();
+      stylesheet.replaceSync(`
+        :host {
+          position: fixed;
+          bottom: 1em;
+          right: 1em;
+          border: solid;
+          padding: 1em;
+          background: white;
+          color: black;
+          z-index: 1;
+        }
+
+        :host(:not([open])) {
+          display: none;
+        }
+
+        .default-closebutton {
+          user-select: none;
+        }
+
+        :host([type=success i]) {
+          border-color: green;
+        }
+
+        :host([type=warning i]) {
+          border-color: orange;
+        }
+
+        :host([type=error i]) {
+          border-color: red;
+        }
+      `);
+      // TODO(jacksteinberg): use offset-block-end: / offset-inline-end: over bottom: / right:
+      // when implemented https://bugs.chromium.org/p/chromium/issues/detail?id=538475
+    }
+    return stylesheet;
+  };
+}
+
+const generateStylesheet = stylesheetFactory();
+
+export class StdToastElement extends HTMLElement {
+  static observedAttributes = ['open', 'closebutton'];
+  #shadow = this.attachShadow({mode: 'closed'});
+  #timeoutID;
+  #actionSlot;
+  #closeButtonElement;
+  #setCloseTimeout = duration => {
+    clearTimeout(this.#timeoutID);
+
+    if (duration === Infinity) {
+      this.#timeoutID = null;
+    } else {
+      this.#timeoutID = setTimeout(() => {
+        this.removeAttribute('open');
+      }, duration);
+    }
+  };
+
+  constructor(message) {
+    super();
+
+    this.#shadow.adoptedStyleSheets = [generateStylesheet()];
+
+    this.#shadow.appendChild(document.createElement('slot'));
+
+    this.#actionSlot = document.createElement('slot');
+    this.#actionSlot.setAttribute('name', 'action');
+    this.#shadow.appendChild(this.#actionSlot);
+
+    this.#closeButtonElement = document.createElement('button');
+    this.#closeButtonElement.setAttribute('part', 'closebutton');
+    setDefaultCloseButton(this.#closeButtonElement);
+    this.#shadow.appendChild(this.#closeButtonElement);
+
+    this.#closeButtonElement.addEventListener('click', () => {
+      this.hide();
+    });
+
+    if (message !== undefined) {
+      this.textContent = message;
+    }
+  }
+
+  connectedCallback() {
+    if (!this.hasAttribute('role')) {
+      this.setAttribute('role', 'status');
+    }
+    // TODO(jacksteinberg): use https://github.com/whatwg/html/pull/4658 when implemented
+  }
+
+  get action() {
+    return this.#actionSlot.assignedNodes().length !== 0 ?
+      this.#actionSlot.assignedNodes()[0] :
+      null;
+  }
+
+  set action(val) {
+    const previousAction = this.action;
+    if (val !== null) {
+      if (!isElement(val)) {
+        throw new TypeError('Invalid argument: must be type Element');
+      }
+
+      val.setAttribute('slot', 'action');
+      this.insertBefore(val, previousAction);
+    }
+
+    if (previousAction !== null) {
+      previousAction.remove();
+    }
+  }
+
+  get closeButton() {
+    if (this.hasAttribute('closebutton')) {
+      const closeAttr = this.getAttribute('closebutton');
+      return closeAttr === '' ? true : closeAttr;
+    }
+    return false;
+  }
+
+  set closeButton(val) {
+    if (val === true) {
+      this.setAttribute('closebutton', '');
+    } else if (val === false) {
+      this.removeAttribute('closebutton');
+    } else {
+      this.setAttribute('closebutton', val);
+    }
+  }
+
+  get type() {
+    const typeAttr = this.getAttribute('type');
+    if (typeAttr === null) {
+      return '';
+    }
+
+    const typeAttrLower = typeAttr.toLowerCase();
+
+    if (TYPES.has(typeAttrLower)) {
+      return typeAttrLower;
+    }
+
+    return '';
+  }
+
+  set type(val) {
+    this.setAttribute('type', val);
+  }
+
+  show({duration = DEFAULT_DURATION} = {}) {
+    if (duration <= 0) {
+      throw new RangeError(`Invalid Argument: duration must be greater than 0 [${duration} given]`);
+    }
+
+    this.setAttribute('open', '');
+    this.#setCloseTimeout(duration);
+  }
+
+  hide() {
+    this.removeAttribute('open');
+  }
+
+  toggle(force) {
+    this.toggleAttribute('open', force);
+  }
+
+  attributeChangedCallback(name, oldValue, newValue) {
+    switch (name) {
+      case 'open':
+        if (newValue !== null && oldValue === null) {
+          this.dispatchEvent(new Event('show'));
+        } else if (newValue === null) {
+          this.dispatchEvent(new Event('hide'));
+          this.#setCloseTimeout(Infinity);
+        }
+        break;
+      case 'closebutton':
+        if (newValue !== null) {
+          if (newValue === '') {
+            setDefaultCloseButton(this.#closeButtonElement);
+          } else {
+            replaceDefaultCloseButton(this.#closeButtonElement, newValue);
+          }
+        }
+        // if newValue === null we do nothing, since CSS will hide the button
+        break;
+    }
+  }
+}
+
+reflection.installBool(StdToastElement.prototype, 'open');
+
+customElements.define('std-toast', StdToastElement);
+
+delete StdToastElement.prototype.attributeChangedCallback;
+delete StdToastElement.prototype.observedAttributes;
+delete StdToastElement.prototype.connectedCallback;
+
+export function showToast(message, options = {}) {
+  const toast = new StdToastElement(message);
+
+  const {
+    action,
+    closeButton,
+    type,
+    ...showOptions
+  } = options;
+
+  if (isElement(action)) {
+    toast.action = action;
+  } else if (action !== undefined) {
+    const actionButton = document.createElement('button');
+
+    // Unlike String(), this performs the desired JavaScript ToString operation.
+    // https://gist.github.com/domenic/82adbe7edc4a33a70f42f255479cec39
+    actionButton.textContent = `${action}`;
+
+    actionButton.setAttribute('slot', 'action');
+    toast.appendChild(actionButton);
+  }
+
+  if (closeButton !== undefined) {
+    toast.closeButton = closeButton;
+  }
+
+  if (type !== undefined) {
+    toast.type = type;
+  }
+
+  document.body.append(toast);
+  toast.show(showOptions);
+
+  return toast;
+}
+
+const idGetter =
+  Object.getOwnPropertyDescriptor(Element.prototype, 'id').get;
+function isElement(value) {
+  try {
+    idGetter.call(value);
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+function setDefaultCloseButton(closeButton) {
+  closeButton.setAttribute('aria-label', 'close');
+  closeButton.setAttribute('class', 'default-closebutton');
+  closeButton.textContent = '×';
+}
+
+function replaceDefaultCloseButton(closeButton, value) {
+  closeButton.textContent = value;
+  closeButton.removeAttribute('aria-label');
+  closeButton.removeAttribute('class');
+}
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/virtual-scroller/.eslintrc.js b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/virtual-scroller/.eslintrc.js
new file mode 100644
index 00000000000..90e626a41fc
--- /dev/null
+++ b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/virtual-scroller/.eslintrc.js
@@ -0,0 +1,337 @@
+// Copyright 2019 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+module.exports = {
+  root: true,
+  env: {
+    es6: true,
+    browser: true
+  },
+  'parser': 'babel-eslint',
+  parserOptions: {
+    sourceType: 'module',
+    ecmaVersion: 2019
+  },
+  rules: {
+    'for-direction': 'error',
+    'getter-return': 'error',
+    'no-async-promise-executor': 'error',
+    'no-await-in-loop': 'error',
+    'no-compare-neg-zero': 'error',
+    'no-cond-assign': ['error', 'except-parens'],
+    'no-console': 'error',
+    'no-constant-condition': ['error', {checkLoops: false}],
+    'no-control-regex': 'error',
+    'no-debugger': 'error',
+    'no-dupe-args': 'error',
+    'no-dupe-keys': 'error',
+    'no-duplicate-case': 'error',
+    'no-empty': 'error',
+    'no-empty-character-class': 'error',
+    'no-ex-assign': 'error',
+    'no-extra-boolean-cast': 'error',
+    'no-extra-parens': [
+      'error',
+      'all',
+      {
+        conditionalAssign: false,
+        nestedBinaryExpressions: false,
+        returnAssign: false
+      }
+    ],
+    'no-extra-semi': 'error',
+    'no-func-assign': 'error',
+    'no-inner-declarations': 'off',
+    'no-invalid-regexp': 'error',
+    'no-irregular-whitespace': 'error',
+    'no-misleading-character-class': 'error',
+    'no-obj-calls': 'error',
+    'no-prototype-builtins': 'error',
+    'no-regex-spaces': 'error',
+    'no-sparse-arrays': 'error',
+    'no-template-curly-in-string': 'error',
+    'no-unexpected-multiline': 'error',
+    'no-unreachable': 'error',
+    'no-unsafe-finally': 'off',
+    'no-unsafe-negation': 'error',
+    'use-isnan': 'error',
+    'valid-typeof': 'error',
+    'accessor-pairs': 'error',
+    'array-callback-return': 'error',
+    'block-scoped-var': 'off',
+    'class-methods-use-this': 'off',
+    'complexity': 'off',
+    'consistent-return': 'error',
+    'curly': ['error', 'all'],
+    'default-case': 'off',
+    'dot-location': ['error', 'property'],
+    'dot-notation': 'error',
+    'eqeqeq': 'error',
+    'guard-for-in': 'off',
+    'no-alert': 'error',
+    'no-caller': 'error',
+    'no-case-declarations': 'error',
+    'no-div-regex': 'off',
+    'no-empty-function': 'off',
+    'no-empty-pattern': 'error',
+    'no-eq-null': 'error',
+    'no-eval': 'error',
+    'no-extend-native': 'error',
+    'no-extra-bind': 'error',
+    'no-extra-label': 'error',
+    'no-fallthrough': 'error',
+    'no-floating-decimal': 'error',
+    'no-global-assign': 'error',
+    'no-implicit-coercion': 'error',
+    'no-implicit-globals': 'error',
+    'no-implied-eval': 'error',
+    'no-iterator': 'error',
+    'no-labels': ['error', {allowLoop: true}],
+    'no-lone-blocks': 'error',
+    'no-loop-func': 'error',
+    'no-magic-numbers': ['error', {ignore: [0, 1, 2]}],
+    'no-multi-spaces': ['error', {ignoreEOLComments: true}],
+    'no-multi-str': 'error',
+    'no-new': 'error',
+    'no-new-func': 'error',
+    'no-new-wrappers': 'error',
+    'no-octal': 'error',
+    'no-octal-escape': 'error',
+    'no-param-reassign': 'off',
+    'no-process-env': 'error',
+    'no-proto': 'error',
+    'no-redeclare': 'error',
+    'no-restricted-properties': 'off',
+    'no-return-assign': ['error', 'except-parens'],
+    'no-return-await': 'error',
+    'no-script-url': 'off',
+    'no-self-assign': 'error',
+    'no-self-compare': 'error',
+    'no-sequences': 'error',
+    'no-throw-literal': 'error',
+    'no-unmodified-loop-condition': 'error',
+    'no-unused-expressions': 'error',
+    'no-unused-labels': 'error',
+    'no-useless-call': 'error',
+    'no-useless-concat': 'error',
+    'no-useless-escape': 'error',
+    'no-useless-return': 'error',
+    'no-void': 'error',
+    'no-warning-comments': 'off',
+    'no-with': 'error',
+    'prefer-promise-reject-errors': 'error',
+    'radix': ['error', 'as-needed'],
+    'require-await': 'off',
+    'vars-on-top': 'off',
+    'wrap-iife': ['error', 'outside'],
+    'yoda': ['error', 'never'],
+    'strict': ['error', 'global'],
+    'init-declarations': 'off',
+    'no-delete-var': 'error',
+    'no-label-var': 'error',
+    'no-restricted-globals': 'off',
+    'no-shadow': 'error',
+    'no-shadow-restricted-names': 'error',
+    'no-undef': 'error',
+    'no-undef-init': 'error',
+    'no-undefined': 'off',
+    'no-unused-vars': 'error',
+    'no-use-before-define': ['error', 'nofunc'],
+    'callback-return': 'off',
+    'global-require': 'error',
+    'handle-callback-err': 'error',
+    'no-buffer-constructor': 'error',
+    'no-mixed-requires': ['error', true],
+    'no-new-require': 'error',
+    'no-path-concat': 'error',
+    'no-process-exit': 'error',
+    'no-restricted-modules': 'off',
+    'no-sync': 'off',
+    'array-bracket-newline': ['error', {multiline: true}],
+    'array-bracket-spacing': ['error', 'never'],
+    'array-element-newline': 'off',
+    'block-spacing': ['error', 'always'],
+    'brace-style': [
+      'error',
+      '1tbs',
+      {allowSingleLine: false}
+    ],
+    camelcase: ['error', {properties: 'always'}],
+    'capitalized-comments': 'off',
+    'comma-dangle': ['error', 'always-multiline'],
+    'comma-spacing': [
+      'error',
+      {
+        before: false,
+        after: true
+      }
+    ],
+    'comma-style': ['error', 'last'],
+    'computed-property-spacing': ['error', 'never'],
+    'consistent-this': 'off',
+    'eol-last': 'error',
+    'func-call-spacing': ['error', 'never'],
+    'func-name-matching': 'error',
+    'func-names': 'off',
+    'func-style': ['error', 'declaration'],
+    'function-paren-newline': 'off',
+    'id-blacklist': 'off',
+    'id-length': 'off',
+    'id-match': 'off',
+    indent: 'off', // not really compatible with clang-format
+    'jsx-quotes': 'off',
+    'key-spacing': [
+      'error',
+      {
+        beforeColon: false,
+        afterColon: true,
+        mode: 'strict'
+      }
+    ],
+    'keyword-spacing': [
+      'error',
+      {
+        before: true,
+        after: true
+      }
+    ],
+    'line-comment-position': 'off',
+    'linebreak-style': ['error', 'unix'],
+    'lines-around-comment': 'off',
+    'max-depth': 'off',
+    'max-len': ['error', {
+        tabWidth: 2,
+        ignorePattern: "(^import |// eslint-disable-line )"}],
+    'max-lines': 'off',
+    'max-nested-callbacks': 'off',
+    'max-params': 'off',
+    'max-statements': 'off',
+    'max-statements-per-line': ['error', {max: 1}],
+    'multiline-ternary': ['error', 'always-multiline'],
+    'new-cap': 'error',
+    'new-parens': 'error',
+    'newline-per-chained-call': 'off',
+    'no-array-constructor': 'error',
+    'no-bitwise': 'off',
+    'no-continue': 'off',
+    'no-inline-comments': 'off',
+    'no-mixed-operators': [
+      'error',
+      {
+        groups: [
+          ['&', '|', '^', '~', '<<', '>>', '>>>'],
+          ['==', '!=', '===', '!==', '>', '>=', '<', '<='],
+          ['&&', '||'],
+          ['in', 'instanceof']
+        ]
+      }
+    ],
+    'no-mixed-spaces-and-tabs': 'error',
+    'no-multi-assign': 'off',
+    'no-multiple-empty-lines': 'error',
+    'no-negated-condition': 'off',
+    'no-nested-ternary': 'error',
+    'no-new-object': 'error',
+    'no-plusplus': 'off',
+    'no-restricted-syntax': 'off',
+    'no-tabs': 'error',
+    'no-ternary': 'off',
+    'no-trailing-spaces': 'error',
+    'no-underscore-dangle': 'off',
+    'no-unneeded-ternary': 'error',
+    'no-whitespace-before-property': 'error',
+    'nonblock-statement-body-position': 'error',
+    'object-curly-newline': ['error', {consistent: true}],
+    'object-curly-spacing': ['error', 'never'],
+    'object-property-newline': 'off',
+    'one-var': ['error', 'never'],
+    'one-var-declaration-per-line': ['error', 'initializations'],
+    'operator-assignment': ['error', 'always'],
+    'operator-linebreak': ['error', 'after'],
+    'padded-blocks': ['error', 'never'],
+    'padding-line-between-statements': 'off',
+    'quote-props': ['error', 'as-needed'],
+    quotes: [
+      'error',
+      'single',
+      {
+        avoidEscape: true,
+        allowTemplateLiterals: true
+      }
+    ],
+    semi: ['error', 'always'],
+    'semi-spacing': 'error',
+    'semi-style': 'error',
+    'sort-keys': 'off',
+    'sort-vars': 'off',
+    'space-before-blocks': ['error', 'always'],
+    'space-before-function-paren': [
+      'error',
+      {
+        anonymous: 'always',
+        named: 'never'
+      }
+    ],
+    'space-in-parens': ['error', 'never'],
+    'space-infix-ops': 'error',
+    'space-unary-ops': [
+      'error',
+      {
+        words: true,
+        nonwords: false
+      }
+    ],
+    'spaced-comment': ['error', 'always'],
+    'switch-colon-spacing': 'error',
+    'template-tag-spacing': 'error',
+    'unicode-bom': 'error',
+    'wrap-regex': 'off',
+    'arrow-body-style': 'off',
+    'arrow-parens': ['error', 'as-needed'],
+    'arrow-spacing': 'error',
+    'constructor-super': 'error',
+    'generator-star-spacing': ['error', 'neither'],
+    'no-class-assign': 'error',
+    'no-confusing-arrow': 'off',
+    'no-const-assign': 'error',
+    'no-dupe-class-members': 'error',
+    'no-duplicate-imports': 'error',
+    'no-new-symbol': 'error',
+    'no-restricted-imports': 'off',
+    'no-this-before-super': 'error',
+    'no-useless-computed-key': 'error',
+    'no-useless-constructor': 'error',
+    'no-useless-rename': 'error',
+    'no-var': 'error',
+    'object-shorthand': 'error',
+    'prefer-arrow-callback': 'error',
+    'prefer-const': ['error', {ignoreReadBeforeAssign: true}],
+    'prefer-destructuring': [
+      'error',
+      {
+        VariableDeclarator: {
+          array: false,
+          object: true
+        },
+        AssignmentExpression: {
+          array: false,
+          object: false
+        }
+      },
+      {
+        enforceForRenamedProperties: false
+      }
+    ],
+    'prefer-numeric-literals': 'error',
+    'prefer-rest-params': 'error',
+    'prefer-spread': 'error',
+    'prefer-template': 'off',
+    'require-yield': 'error',
+    'rest-spread-spacing': 'error',
+    'sort-imports': 'off',
+    'symbol-description': 'error',
+    'template-curly-spacing': ['error', 'never'],
+    'yield-star-spacing': ['error', 'after']
+  }
+};
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/virtual-scroller/OWNERS b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/virtual-scroller/OWNERS
new file mode 100644
index 00000000000..d76cdfa11f0
--- /dev/null
+++ b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/virtual-scroller/OWNERS
@@ -0,0 +1 @@
+fergal@chromium.org
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/virtual-scroller/docs/README.md b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/virtual-scroller/docs/README.md
new file mode 100644
index 00000000000..c5ea6fc86c3
--- /dev/null
+++ b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/virtual-scroller/docs/README.md
@@ -0,0 +1,297 @@
+# Virtual Scroller Notes
+
+This is Blink's implementation of the [`<virtual-scroller>`](https://github.com/WICG/virtual-scroller) element.
+
+## Status
+
+This is a prototype with many known issues.
+
+## Principles
+
+- Avoid operations that are O(number of children)
+- Ensure that we only perform operations that cause DOM, style or rendering work in the browser
+  that is O(number of visible elements).
+- Avoid forcing layout from JS.
+
+## Current Implementation Strategy
+
+The prototype uses a custom element implemented in JS.
+It only handles vertical block layout,
+so this talks only about height.
+This custom element manages the display-locking status of its child items.
+It considers a range of pixels to be the "unlocked range".
+This range is determined from the window size.
+
+TODO(crbug.com/983052): Be smarter about determining the buffer size,
+given that the window can be resized.
+
+Items which are within the unlocked range are left unlocked.
+All other items are locked
+so that they do not incur style and rendering costs for their contents.
+They are locked with a height that is our best guess at their rendered height.
+This guess is based on
+- a fixed default
+- a previously measured height of this item
+- an average of previous observed heights of items
+
+The virtual scroller listens to observers to know when it needs to reconsider which items should be locked.
+It keeps a resize observer on itself since if it is resized,
+items may need to be newly locked or unlocked.
+It keeps an intersection observer on all unlocked child items.
+Along with the buffer around the screen,
+this allows it to know when the state has changed such that we may need to lock or unlock different items.
+
+TODO(crbug.com/983050): Observe one item above and below the unlocked items too,
+without this, if the edge item is larger than the window,
+we can scroll empty space into the visible region.
+
+TODO(crbug.com/983046): Keep an intersection observer on the scroller.
+This allows us to know whether the scroller is offscreen.
+In that case we lock all elements
+and pause all activity.
+This includes if the scroller is contained in a locked element
+(e.g. nested in another virtual scroller).
+
+The virtual scroller keeps a mutation observer on itself
+so that it can react to elements being added, removed or moved around.
+When dealing with mutations,
+elements which are newly added are treated differently
+to elements which are removed and re-added.
+Newly added elements are immediately locked.
+This allows a large number of elements to be added,
+without a large rendering/style cost for these elements.
+
+The virtual scroller does not listen directly for scroll events
+and does not know or care whether it is in a scrollable region.
+It is tempting to try discover whether the scroller is contained in a scrolling region
+and then listen for scroll events,
+however the scroller may be contained in any number of nested scrollable regions
+and DOM changes can cause it to be reparented.
+Also, we only need to change state when an item enters or leaves the visible range
+but scroll events may occur much more frequently than that.
+
+The virtual scroller takes no action directly in response to these events.
+It simply ensures that a `requestAnimationFrame` (RAF) callback will run this frame
+(max one per frame).
+This callback is the "sync" callback.
+It will attempt to react to the new state of the world
+and try to ensure that the scroller is in sync with it.
+This is where we determine which elements to lock or unlock.
+
+When determining which items should be locked and which should be unlocked,
+the virtual scroller uses `getBoundingClientRect`
+to get the coordinates of its items,
+relative to the root viewport.
+It binary searches on the array of items
+to find the element at the top and bottom of the visible range.
+At the end of the sync,
+these and the elements in between them will be unlocked
+and all other elements will be locked.
+The scroller knows which elements are currently unlocked
+and does the minimal amount of locking and unlocking
+to bring it to the desired state.
+Also the intersection observers will be updated to match this range of elements.
+
+It is very possible that the range of elements we have unlocked
+is too big or too small for the viewport.
+We cannot know the rendered size of these elements
+until we have unlocked and measured them.
+In order to avoid extra forced layouts,
+we simply queue another sync callback for the next frame.
+We continue to queue sync callbacks until one of them makes no changes.
+
+Internally, the virtual scroller slots all children into a single slot.
+It changes the locked state of the light tree children directly.
+
+## Known issues specific to the current prototype
+
+### Display locking items directly
+
+The current prototype changes the locked state of the light tree children directly.
+This means that the scroller's actions can be detected from outside.
+It also means that an author cannot (in general) safely use display locking
+on the children of a virtual scroller.
+
+Other approaches do not have this issue,
+because they slot the items into more than one slot,
+however, this requires either manipulating the `slot` attribute on the items
+or [imperative slotting](https://www.chromestatus.com/feature/5711021289242624).
+
+### Binary searching the items
+
+The first problem with this is that it requires forced layout (see below).
+
+The second (potential) problem is that
+while JS presents an `Array` interface for the children of the virtual scroller,
+the reality is that in Blink,
+the elements are stored in a linked list
+with some extra logic to remember the most recent indexed access
+and use that to speed up subsequent index accesses
+(e.g. accessing `[n+1]` after `[n]` is fast).
+This makes the binary search actually O(number of children)
+because the C++ code must traverse a linked list.
+However C++ traversing a link list is very fast
+so this tends not to be noticeable.
+
+### Locked elements still have a cost
+
+While the descendants of locked elements are skipped for style and layout,
+the locked elements themselves are still traversed
+and participate in style and layout.
+In the scroller,
+the elements are locked with a size
+and behave just as an empty div with that size.
+This means that when we add many children to the virtual scroller,
+even though most of them are locked,
+there can still be quite a large style and rendering cost
+from the locked elements in aggregate.
+
+## Known issues common to many approaches
+
+### Intersection observers are slow
+
+Intersection observers signal the intersection state *after* it has happened.
+This means that by only reacting to intersection observers,
+the scroller may react late to scrolls and jumps.
+Once a scroll begins,
+it's likely that the element will keep up,
+since it is not using the details of the events to compute the state of the scroller.
+
+### Forced layouts to measure item sizes
+
+After unlocking, the scroller needs to know the rendered size of an element.
+In order to do that it must call `getBoundingClientRect`.
+This forces the browser to have clean style and layout
+for all unlocked elements in the document
+(whether this is expensive depends on what has changed since the last time layout).
+It may be better to perform these measurements in a
+[post animation frame callback](https://github.com/WICG/requestPostAnimationFrame/blob/master/explainer.md)
+when that feature becomes available
+because this callback guarantees that style and layout are clean,
+so measuring elements should be inexpensive.
+
+## Alternative approaches
+
+### Unlocked tree of divs with `<slot>`s for leaves (rejected)
+
+We could avoid the O(number of children) run of locked divs
+by building a tree of divs (e.g. a binary tree)
+and locking all of the slots except those containing the visible items.
+
+*PROBLEM:* This breaks margin collapsing between items
+and maybe other layout or style features.
+In order to make margin collapsing work correctly
+we would need to make all of the divs in this tree have style `display: contents`
+but for layout, this would have exactly the same performance problem as placing them all as siblings in one slot.
+
+### One visible slot in the middle (rejected)
+
+We could assign all of the visible items to a single slot,
+ensuring they behave correctly with respect to margin collapsing
+and keep all other items in other slots.
+
+We need to ensure that elements are slotted in their light-tree order
+for find-in-page, accessibility etc to work correctly.
+The simplest form of this is a three-slot approach
+with one slot for the invisible items at the top,
+another slot for the visible items in the middle
+and a third slot for the invisible items at the bottom.
+The top and bottom slot remain locked always
+and items are moved into the visible slot when they should be visible.
+The top and bottom slots are inside a locked div.
+These divs are locked with a size estimated to be the correct aggregate size for their slotted elements.
+
+*PROBLEM:* Gradually scrolling down moves items one at a time
+from the bottom slot, to the visible slot and then into the top slot
+but long-range jumps require moving O(number of children) items between slots.
+E.g. if the top items are visible and we jump to make the bottom items visible,
+then we have to assign almost all of the items that were in the bottom slot to the top slot.
+
+### Roaming visible slot (not preferred)
+
+This is similar to [One visible slot in the middle](#One-visible-slot-in-the-middle) approach
+but rather than a top and bottom slot,
+item assignment is divided over many slots.
+Each item has a natural "leaf" slot that it should be assigned to.
+All of the leaf slots are kept locked.
+There is a single visible slot that contains the currently unlocked items
+and it roams around between the leaf slots
+to ensure that order is correct for find-in-page etc.
+If we keep the number of items per slot low,
+then long jumps never cause a large number of items to be reassigned,
+at worst we need to reassign the currently visible items back to their leaf slots,
+move the visible slot to a new place
+and fill it with newly visible items.
+
+It's possible that there will be so many slots
+that once again we run into the problem of large numbers of empty divs.
+So we may need to maintain a tree of divs and `<slot>`s.
+Most of this tree would be locked
+but the path from the visible slot to the root would be unlocked.
+
+It looks like this:
+
+![Diagram of a sample roaming visible slot tree](roaming-slot.png)
+
+Original diagram [here](https://docs.google.com/drawings/d/1oZ8U16GzkxO3GaYLDygPsrmXiHO7SLNFXvVUK6WkG4I/edit)
+
+*CHALLENGES:* This approach does not seem to have any insurmountable problems,
+however it is not simple:
+- We need to ensure that the tree remains balanced in the face of mutations of the virtual scrollers contents.
+- A tree may introduce a large number of tree-only elements.
+  With a binary tree, this would be equal to the number of items in the scroller.
+  It might be worth using a larger branching factor, to reduce this cost.
+  E.g. in a 10-way tree the overhead is only 1/9 the number of leaves.
+- There is a lot of re-slotting of items.
+- The visible slot may contain a large number of elements (if elements are small)
+  and Blink has some [optimizations](https://cs.chromium.org/chromium/src/third_party/blink/renderer/core/html/html_slot_element.cc?q=symbol:HTMLSlotElement::NotifySlottedNodesOfFlatTreeChange)
+  that only work when slots contain <= 16 elements.
+- Adding slots and/or assigning elements to slots currently involves operations that are O(number of children).
+  Adding N slots can take O(N^2) time.
+  This was previously not a concern in Blink
+  because, in general, the style and layout costs dominated.
+  However display locking eliminates these costs,
+  leaving the slotting costs as the bottleneck when there are large numbers of items.
+
+### One slot per item (most promising alternative)
+
+This is similar to [Roaming visible slot](#Roaming-visible-slot).
+We have a tree of divs with slots as leaves
+but in this approach we have exactly one slot per item.
+For any item that should be unlocked,
+we ensure that all of its tree ancestors are unlocked
+and have style `display: contents`.
+All other nodes in the tree have style `display: block; contain: style layout`,
+to allow them to be locked.
+
+This has the effect of making all of the visible items siblings,
+from the perspective of layout,
+so that margin collapsing, etc. works correctly.
+It also ensures that not only are the invisible items and tree divs locked
+but they are *inside* locked ancestors,
+so do not incur *any* costs.
+
+There is no need to maintain spacer divs above and below the visible region.
+Instead, when we lock any tree element,
+we set its locked size to be its current visible size.
+If its contents don't change then this element has the correct aggregate size for its contents.
+If this element's parent is unlocked then this correct size will be used in sizing the parent.
+
+Mutations to the tree require size updates to propagate up the ancestor chain.
+E.g. inserting an element causes all of the elements ancestors to grow by our best guess at its size.
+So, the initial state of the tree
+(which comes from an initial insert)
+is that everything is an estimate or sum of estimates,
+with the sizes getting more accurate
+as more elements are rendered, measured and re-locked with correct sizes.
+
+It's likely that the sizes above will be off by some amount due to margins
+but they should be good enough for maintaining a usable scrollbar.
+
+*CHALLENGES:* This approach does not seem to have any insurmountable problems,
+however it is not so simple.
+It has a subset of the challenges of [Roaming visible slot](#Roaming-visible-slot):
+
+- Needs a balanced tree.
+- Possible large number of tree-only elements.
+- Slot performance issues.
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/virtual-scroller/docs/roaming-slot.png b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/virtual-scroller/docs/roaming-slot.png
new file mode 100644
index 00000000000..2f9b6844694
--- /dev/null
+++ b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/virtual-scroller/docs/roaming-slot.png
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/virtual-scroller/find-element.mjs b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/virtual-scroller/find-element.mjs
new file mode 100644
index 00000000000..c25edc0a7fd
--- /dev/null
+++ b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/virtual-scroller/find-element.mjs
@@ -0,0 +1,104 @@
+/**
+ * Copyright 2019 The Chromium Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ *
+ * @fileoverview Utilities for binary searching by layed-out pixed offset in a
+ * list of elements.
+ * @package
+ */
+
+/** Symbols for use with @see findElement */
+export const BIAS_LOW = Symbol('BIAS_LOW');
+export const BIAS_HIGH = Symbol('BIAS_HIGH');
+
+function getBound(elements, edgeIndex) {
+  const element = elements[Math.floor(edgeIndex / 2)];
+  const rect = element.getBoundingClientRect();
+  return edgeIndex % 2 ? rect.bottom : rect.top;
+}
+
+/**
+ * Does the actual work of binary searching. This searches amongst the 2*N edges
+ * of the N elements. Returns the index of an edge found, 2i is the low edge of
+ * the ith element, 2i+1 is the high edge of the ith element. If |bias| is low
+ * then we find the index of the lowest edge >= offset. Otherwise we find index
+ * of the highest edge > offset.
+ */
+function findEdgeIndex(elements, offset, bias) {
+  let low = 0;
+  let high = elements.length * 2 - 1;
+  while (low < high) {
+    const i = Math.floor((low + high) / 2);
+    const bound = getBound(elements, i);
+    if (bias === BIAS_LOW) {
+      if (bound < offset) {
+        low = i + 1;
+      } else {
+        high = i;
+      }
+    } else {
+      if (offset < bound) {
+        high = i;
+      } else {
+        low = i + 1;
+      }
+    }
+  }
+  return low;
+}
+
+/**
+ * Binary searches inside the array |elements| to find an element containing or
+ * nearest to |offset| (based on @see Element#getBoundingClientRect()). Assumes
+ * that the elements are already sorted in increasing pixel order. |bias|
+ * controls what happens if |offset| is not contained within any element or if
+ * |offset| is contained with 2 elements (this only happens if there is no
+ * margin between the elements). If |bias| is BIAS_LOW, then this selects the
+ * lower element nearest |offset|, otherwise it selects the higher element.
+ *
+ * Returns null if |offset| is not within any element.
+ *
+ * @param {!Element[]} elements An array of Elements in display order,
+ *     i.e. the pixel offsets of later element are higher than those of earlier
+ *     elements.
+ * @param {!number} offset The target offset in pixels to search for.
+ * @param {!Symbol} bias Controls whether we prefer a higher or lower element
+ *     when there is a choice between two elements.
+ */
+export function findElement(elements, offset, bias) {
+  if (elements.length === 0) {
+    return null;
+  }
+  // Check if the offset is outside the range entirely.
+  if (offset < getBound(elements, 0) ||
+      offset > getBound(elements, elements.length * 2 - 1)) {
+    return null;
+  }
+
+  let edgeIndex = findEdgeIndex(elements, offset, bias);
+
+  // Fix up edge cases.
+  if (bias === BIAS_LOW) {
+    // bound(0)..bound(edgeIndex) < offset <= bound(edgeIndex+1) ...
+    // If we bias low and we got a low edge and we weren't exactly on the edge
+    // then we want to select the element that's lower.
+    if (edgeIndex % 2 === 0) {
+      const bound = getBound(elements, edgeIndex);
+      if (offset < bound) {
+        edgeIndex--;
+      }
+    }
+  } else {
+    // bound(0)..bound(edgeIndex - 1) <= offset < bound(edgeIndex) ...
+    // If we bias high and we got a low edge, we need to check if we were
+    // exactly on the edge of the previous element.
+    if (edgeIndex % 2 === 0) {
+      const bound = getBound(elements, edgeIndex - 1);
+      if (offset === bound) {
+        edgeIndex--;
+      }
+    }
+  }
+  return elements[Math.floor(edgeIndex / 2)];
+}
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/virtual-scroller/index.mjs b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/virtual-scroller/index.mjs
new file mode 100644
index 00000000000..daef60f7232
--- /dev/null
+++ b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/virtual-scroller/index.mjs
@@ -0,0 +1,57 @@
+/**
+ * Copyright 2019 The Chromium Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ *
+ * @fileoverview This file defines virtual-scroller element.
+ * EXPLAINER: https://github.com/fergald/virtual-scroller/blob/master/README.md
+ * TEST PATH: third_party/blink/web_tests/http/tests/virtual-scroller/*
+ *            third_party/blink/web_tests/wpt_internal/virtual-scroller/*
+ * @package
+ */
+import {VisibilityManager} from './visibility-manager.mjs';
+
+function styleSheetFactory() {
+  let styleSheet;
+  return () => {
+    if (!styleSheet) {
+      styleSheet = new CSSStyleSheet();
+      styleSheet.replaceSync(`
+:host {
+  display: block;
+}
+
+::slotted(*) {
+  display: block !important;
+  contain: layout style;
+}
+`);
+    }
+    return styleSheet;
+  };
+}
+
+/**
+ * The class backing the virtual-scroller custom element.
+ */
+export class VirtualScrollerElement extends HTMLElement {
+  constructor() {
+    super();
+
+    const shadowRoot = this.attachShadow({mode: 'closed'});
+    shadowRoot.adoptedStyleSheets = [styleSheetFactory()()];
+    shadowRoot.appendChild(document.createElement('slot'));
+
+    const visibilityManager = new VisibilityManager(this.children);
+
+    new ResizeObserver(() => {
+      visibilityManager.scheduleSync();
+    }).observe(this);
+
+    new MutationObserver(records => {
+      visibilityManager.applyMutationObserverRecords(records);
+    }).observe(this, {childList: true});
+  }
+}
+
+customElements.define('virtual-scroller', VirtualScrollerElement);
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/virtual-scroller/sets.mjs b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/virtual-scroller/sets.mjs
new file mode 100644
index 00000000000..9b1aff8eca1
--- /dev/null
+++ b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/virtual-scroller/sets.mjs
@@ -0,0 +1,24 @@
+/**
+ * Copyright 2019 The Chromium Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ *
+ * @fileoverview Utility functions for set operations.
+ * @package
+ */
+
+/*
+ * Returns the set of elements in |a| that are not in |b|.
+ *
+ * @param {!Set} a A set of elements.
+ * @param {!Set} b A set of elements.
+*/
+export function difference(a, b) {
+  const result = new Set();
+  for (const element of a) {
+    if (!b.has(element)) {
+      result.add(element);
+    }
+  }
+  return result;
+}
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/virtual-scroller/visibility-manager.mjs b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/virtual-scroller/visibility-manager.mjs
new file mode 100644
index 00000000000..ecc160f9f0d
--- /dev/null
+++ b/chromium/third_party/blink/renderer/core/script/resources/layered_api/elements/virtual-scroller/visibility-manager.mjs
@@ -0,0 +1,407 @@
+/**
+ * Copyright 2019 The Chromium Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ *
+ * @fileoverview This file provides the class backing the virtual-scroller
+ *    element.
+ * @package
+ */
+import * as sets from './sets.mjs';
+import * as findElement from './find-element.mjs';
+
+
+// This controls how much above and below the current screen we
+// reveal, e.g. 1 = 1 screen of content.
+const BUFFER = 0.2;
+// When we know about the heights of elements we default this height.
+const DEFAULT_HEIGHT_ESTIMATE_PX = 100;
+// When we lock an element, we use this as the width. We use 1px because locked
+// items will not resize when their container changes and so could result in a
+// horizontal scroll-bar appearing if it they are wide enough.
+const LOCKED_WIDTH_PX = 1;
+
+/**
+ * Represents a range of elements from |low| to |high|, inclusive.
+ * If either |low| or |high| are null then we treat this as an empty range.
+ */
+class ElementBounds {
+  /** @const {Element} */
+  low;
+  /** @const {Element} */
+  high;
+
+  constructor(low, high) {
+    this.low = low;
+    this.high = high;
+  }
+
+  // Returns a Set containing all of the elements from low to high.
+  elementSet() {
+    const result = new Set();
+    if (this.low === null || this.high === null) {
+      return result;
+    }
+    let element = this.low;
+    while (element) {
+      result.add(element);
+      if (element === this.high) {
+        break;
+      }
+      element = element.nextElementSibling;
+    }
+    return result;
+  }
+}
+
+const EMPTY_ELEMENT_BOUNDS = new ElementBounds(null, null);
+
+/**
+ * Manages measuring and estimating sizes of elements.
+ *
+ * This tracks an average measured element size as elements are added
+ * and removed.
+*/
+class SizeManager {
+  #sizes = new WeakMap();
+
+  #totalMeasuredSize = 0;
+  #measuredCount = 0;
+
+  /**
+   * Measures and stores |element|'s size. If |element| was measured
+   * previously, this updates everything to use the new current size.
+   *
+   * @param {!Element} element The element to measure.
+   */
+  measure(element) {
+    let oldSize = this.#sizes.get(element);
+    if (oldSize === undefined) {
+      oldSize = 0;
+      this.#measuredCount++;
+    }
+    const newSize = element.getBoundingClientRect().height;
+    this.#totalMeasuredSize += newSize - oldSize;
+    this.#sizes.set(element, newSize);
+  }
+
+  /**
+   * Returns a size for |element|, either the last stored size or an
+   * estimate based on all other previously measured elements or a
+   * default.
+   *
+   * @param {!Element} element The element to produce a size for.
+   */
+  getHopefulSize(element) {
+    const size = this.#sizes.get(element);
+    return size === undefined ? this.#getAverageSize() : size;
+  }
+
+  #getAverageSize = () => {
+    return this.#measuredCount > 0 ?
+      this.#totalMeasuredSize / this.#measuredCount :
+      DEFAULT_HEIGHT_ESTIMATE_PX;
+  }
+
+  /**
+   * Removes all data related to |element| from the manager.
+   *
+   * @param {!Element} element The element to remove.
+   */
+  remove(element) {
+    const oldSize = this.#sizes.get(element);
+    if (oldSize === undefined) {
+      return;
+    }
+    this.#totalMeasuredSize -= oldSize;
+    this.#measuredCount--;
+    this.#sizes.delete(element);
+  }
+}
+
+/**
+ * Manages the visibility (locked/unlocked state) of a list of
+ * elements. This list of elements is assumed to be in vertical
+ * display order (e.g. from lowest to highest offset).
+ *
+ * It uses resize and intersection observers on all of the visible
+ * elements to ensure that changes that impact visibility cause us to
+ * recalulate things (e.g. scrolling, restyling).
+*/
+export class VisibilityManager {
+  #sizeManager = new SizeManager();
+  #elements;
+  #syncRAFToken;
+
+  #elementIntersectionObserver;
+  #elementResizeObserver;
+
+  #revealed = new Set();
+
+  constructor(elements) {
+    this.#elements = elements;
+
+    // We want to sync if any element's size changes or if it becomes
+    // more/less visible.
+    this.#elementIntersectionObserver = new IntersectionObserver(() => {
+      this.scheduleSync();
+    });
+    // TODO(fergal): Remove this? I'm not sure that we need the resize
+    // observer. Any resize that is important to us seems like it will
+    // also involve an intersection change.
+    this.#elementResizeObserver = new ResizeObserver(() => {
+      this.scheduleSync();
+    });
+
+    for (const element of this.#elements) {
+      this.#didAdd(element);
+    }
+    this.scheduleSync();
+  }
+
+  /**
+   * Attempts to unlock a range of elements suitable for the current
+   * viewport. This causes one forced layout.
+   */
+  #sync = () => {
+    if (this.#elements.length === 0) {
+      return;
+    }
+
+    // The basic idea is ...
+    // The forced layout occurs at the start. We then use the laid out
+    // coordinates (which are based on a mix of real sizes for
+    // unlocked elements and the estimated sizes at the time of
+    // locking for locked elements) to calculate a set of elements
+    // which should be revealed. We use unlock/lock to move to this
+    // new set of revealed elements. We will check in the next frame
+    // whether we got it correct.
+
+    // This causes a forced layout and takes measurements of all
+    // currently revealed elements.
+    this.#measureRevealed();
+
+    // Compute the pixel bounds of what we would like to reveal. Then
+    // find the elements corresponding to these bounds.
+    // TODO(fergal): Use nearest scrolling ancestor?
+    const desiredLow = 0 - window.innerHeight * BUFFER;
+    const desiredHigh = window.innerHeight + window.innerHeight * BUFFER;
+    const newBounds = this.#findElementBounds(desiredLow, desiredHigh);
+    const newRevealed = newBounds.elementSet();
+
+    // TODO(fergal): We need to observe 1 element off the end of the
+    // list, to cope with e.g. the scrolling region suddenly growing.
+
+    // Lock and unlock the minimal set of elements to get us to the
+    // new state.
+    const toHide = sets.difference(this.#revealed, newRevealed);
+    toHide.forEach(e => this.#hide(e));
+    const toReveal = sets.difference(newRevealed, this.#revealed);
+    toReveal.forEach(e => this.#reveal(e));
+
+    // Now we have revealed what we hope will fill the screen. It
+    // could be incorrect. Rather than measuring now and correcting it
+    // which would involve an unknown number of forced layouts, we
+    // come back next frame and try to make it better. We know we can
+    // stop when we didn't hide or reveal any elements.
+    if (toHide.size > 0 || toReveal.size > 0) {
+      this.scheduleSync();
+    }
+  }
+
+  /**
+   * Searches within the managed elements and returns an ElementBounds
+   * object. This object may represent an empty range or a range whose low
+   * element contains or is lower than |low| (or the lowest element
+   * possible). Similarly for |high|.
+   *
+   * @param {!number} low The lower bound to locate.
+   * @param {!number} high The upper bound to locate.
+   */
+  #findElementBounds = (low, high) => {
+    const lowElement = findElement.findElement(
+        this.#elements, low, findElement.BIAS_LOW);
+    const highElement = findElement.findElement(
+        this.#elements, high, findElement.BIAS_HIGH);
+
+    if (lowElement === null) {
+      if (highElement === null) {
+        return EMPTY_ELEMENT_BOUNDS;
+      } else {
+        return new ElementBounds(this.#elements[0], highElement);
+      }
+    } else if (highElement === null) {
+      return new ElementBounds(
+          lowElement, this.#elements[this.#elements.length - 1]);
+    }
+    return new ElementBounds(lowElement, highElement);
+  }
+
+  /**
+   * Updates the size manager with all of the currently revealed
+   * elements' sizes. This will cause a forced layout.
+   */
+  #measureRevealed = () => {
+    for (const element of this.#revealed) {
+      this.#sizeManager.measure(element);
+    }
+  }
+
+  /**
+   * Reveals |element| so that it can be rendered. This includes
+   * unlocking and adding to various observers.
+   *
+   * @param {!Element} element The element to reveal.
+   */
+  #reveal = element => {
+    this.#revealed.add(element);
+    this.#elementIntersectionObserver.observe(element);
+    this.#elementResizeObserver.observe(element);
+    this.#unlock(element);
+  }
+
+  #logLockingError = (operation, reason, element) => {
+    // TODO: Figure out the LAPIs error/warning logging story.
+    console.error('Rejected: ', operation, element, reason);  // eslint-disable-line no-console
+  }
+
+  /**
+   * Unlocks |element|.
+   *
+   * @param {!Element} element The element to unlock.
+   */
+  #unlock = element => {
+    element.displayLock.commit().catch(reason => {
+      // Only warn if the unlocked failed and we should be revealed.
+      if (this.#revealed.has(element)) {
+        this.#logLockingError('Commit', reason, element);
+      }
+    });
+  }
+
+  /**
+   * Hides |element| so that it cannot be rendered. This includes
+   * locking and removing from various observers.
+   *
+   * @param {!Element} element The element to hide.
+   */
+  #hide = element => {
+    this.#revealed.delete(element);
+    this.#elementIntersectionObserver.unobserve(element);
+    this.#elementResizeObserver.unobserve(element);
+    element.displayLock.acquire({
+      timeout: Infinity,
+      activatable: true,
+      size: [LOCKED_WIDTH_PX, this.#sizeManager.getHopefulSize(element)],
+    }).catch(reason => {
+      // Only warn if the lock failed and we should be locked.
+      if (!this.#revealed.has(element)) {
+        this.#logLockingError('Acquire', reason, element);
+      }
+    });
+  }
+
+  /**
+   * Notify the manager that |element| has been added to the list of
+   * managed elements.
+   *
+   * @param {!Element} element The element that was added.
+   */
+  #didAdd = element => {
+    // Added children should be invisible initially. We want to make them
+    // invisible at this MutationObserver timing, so that there is no
+    // frame where the browser is asked to render all of the children
+    // (which could be a lot).
+    this.#hide(element);
+  }
+
+  /**
+   * Notify the manager that |element| has been removed from the list
+   * of managed elements.
+   *
+   * @param {!Element} element The element that was removed.
+   */
+  #didRemove = element => {
+    // Removed children should be made visible again. We should stop
+    // observing them and discard any size info we have for them as it
+    // may have become incorrect.
+    //
+    // TODO(fergal): Decide whether to also unlock if
+    // displayLock.locked is true. That would only be necessary if we
+    // got out of sync between this.#revealed and the locked state. So
+    // for now, assume are not buggy.
+    if (this.#revealed.has(element)) {
+      this.#unlock(element);
+    }
+    this.#revealed.delete(element);
+    this.#elementIntersectionObserver.unobserve(element);
+    this.#elementResizeObserver.unobserve(element);
+    this.#sizeManager.remove(element);
+  }
+
+  /**
+   * Ensures that @see #sync() will be called at the next animation frame.
+   */
+  scheduleSync() {
+    if (this.#syncRAFToken !== undefined) {
+      return;
+    }
+
+    this.#syncRAFToken = window.requestAnimationFrame(() => {
+      this.#syncRAFToken = undefined;
+      this.#sync();
+    });
+  }
+
+  /**
+   * Applys |records| generated by a mutation event to the manager.
+   * This computes the elements that were newly added/removed and
+   * notifies the managers for each.
+   *
+   * @param {!Object} records The mutations records.
+   */
+  applyMutationObserverRecords(records) {
+    // It's unclear if we can support children which are not
+    // elements. We cannot control their visibility using display
+    // locking but we can just leave them alone.
+    //
+    // Relevant mutations are any additions or removals, including
+    // non-elements and also elements that are removed and then
+    // re-added as this may impact element bounds.
+    let relevantMutation = false;
+    const toRemove = new Set();
+    for (const record of records) {
+      relevantMutation = relevantMutation || record.removedNodes.length > 0;
+      for (const node of record.removedNodes) {
+        if (node.nodeType === Node.ELEMENT_NODE) {
+          toRemove.add(node);
+        }
+      }
+    }
+
+    const toAdd = new Set();
+    for (const record of records) {
+      relevantMutation = relevantMutation || record.addedNodes.length > 0;
+      for (const node of record.addedNodes) {
+        if (node.nodeType === Node.ELEMENT_NODE) {
+          if (toRemove.has(node)) {
+            toRemove.delete(node);
+          } else {
+            toAdd.add(node);
+          }
+        }
+      }
+    }
+    for (const node of toRemove) {
+      this.#didRemove(node);
+    }
+    for (const node of toAdd) {
+      this.#didAdd(node);
+    }
+
+    if (relevantMutation) {
+      this.scheduleSync();
+    }
+  }
+}
+
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/kv-storage/async_iterator.mjs b/chromium/third_party/blink/renderer/core/script/resources/layered_api/kv-storage/async_iterator.mjs
index 0da4854b99d..a83dba41c20 100644
--- a/chromium/third_party/blink/renderer/core/script/resources/layered_api/kv-storage/async_iterator.mjs
+++ b/chromium/third_party/blink/renderer/core/script/resources/layered_api/kv-storage/async_iterator.mjs
@@ -16,6 +16,8 @@ const AsyncIteratorPrototype = Object.getPrototypeOf(
 const StorageAreaAsyncIteratorPrototype = {
   __proto__: AsyncIteratorPrototype,
 
+  [Symbol.toStringTag]: 'StorageArea AsyncIterator',
+
   next() {
     const performDatabaseOperation = _performDatabaseOperation.get(this);
     if (!performDatabaseOperation) {
@@ -42,6 +44,12 @@ const StorageAreaAsyncIteratorPrototype = {
   },
 };
 
+Object.defineProperty(
+  StorageAreaAsyncIteratorPrototype,
+  Symbol.toStringTag,
+  {writable: false, enumerable: false}
+);
+
 function getNextIterResult(iter, performDatabaseOperation) {
   return performDatabaseOperation(async (transaction, store) => {
     const lastKey = _lastKey.get(iter);
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/kv-storage/index.mjs b/chromium/third_party/blink/renderer/core/script/resources/layered_api/kv-storage/index.mjs
index b5272ea5d7b..88ef25e818a 100644
--- a/chromium/third_party/blink/renderer/core/script/resources/layered_api/kv-storage/index.mjs
+++ b/chromium/third_party/blink/renderer/core/script/resources/layered_api/kv-storage/index.mjs
@@ -5,16 +5,18 @@
 import {createStorageAreaAsyncIterator} from './async_iterator.mjs';
 import {promiseForRequest, promiseForTransaction, throwForDisallowedKey} from './idb_utils.mjs';
 
-// TODOs/spec-noncompliances:
+// Overall TODOs/spec-noncompliances:
 // - Susceptible to tampering of built-in prototypes and globals. We want to
 //   work on tooling to ameliorate that.
 
 const DEFAULT_STORAGE_AREA_NAME = 'default';
 const DEFAULT_IDB_STORE_NAME = 'store';
 
+// TODO(crbug.com/977470): this should be handled via infrastructure that
+// avoids putting it in the module map entirely, not as a runtime check.
+// Several web platform tests fail because of this.
 if (!self.isSecureContext) {
-  throw new DOMException(
-      'KV Storage is only available in secure contexts', 'SecurityError');
+  throw new TypeError('KV Storage is only available in secure contexts');
 }
 
 export class StorageArea {
@@ -132,8 +134,25 @@ export class StorageArea {
 }
 
 StorageArea.prototype[Symbol.asyncIterator] = StorageArea.prototype.entries;
-
-export const storage = new StorageArea(DEFAULT_STORAGE_AREA_NAME);
+StorageArea.prototype[Symbol.toStringTag] = 'StorageArea';
+
+// Override the defaults that are implied by using class declarations and
+// assignment, to be more Web IDL-ey.
+// https://github.com/heycam/webidl/issues/738 may modify these a bit.
+Object.defineProperties(StorageArea.prototype, {
+  set: {enumerable: true},
+  get: {enumerable: true},
+  delete: {enumerable: true},
+  clear: {enumerable: true},
+  keys: {enumerable: true},
+  values: {enumerable: true},
+  entries: {enumerable: true},
+  backingStore: {enumerable: true},
+  [Symbol.asyncIterator]: {enumerable: false},
+  [Symbol.toStringTag]: {writable: false, enumerable: false}
+});
+
+export default new StorageArea(DEFAULT_STORAGE_AREA_NAME);
 
 async function performDatabaseOperation(
     promise, setPromise, name, mode, steps) {
@@ -145,7 +164,9 @@ async function performDatabaseOperation(
   const transaction = database.transaction(DEFAULT_IDB_STORE_NAME, mode);
   const store = transaction.objectStore(DEFAULT_IDB_STORE_NAME);
 
-  return steps(transaction, store);
+  const result = steps(transaction, store);
+  transaction.commit();
+  return result;
 }
 
 function initializeDatabasePromise(setPromise, databaseName) {
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/resources.grdp b/chromium/third_party/blink/renderer/core/script/resources/layered_api/resources.grdp
index 2a7e3b38f14..255d05543d1 100644
--- a/chromium/third_party/blink/renderer/core/script/resources/layered_api/resources.grdp
+++ b/chromium/third_party/blink/renderer/core/script/resources/layered_api/resources.grdp
@@ -7,14 +7,17 @@
        third_party/blink/public/blink_resources.grd.
     -->
   <include name="IDR_LAYERED_API_BLANK_INDEX_MJS" file="../renderer/core/script/resources/layered_api/blank/index.mjs" type="BINDATA" skip_minify="true" compress="gzip"/>
+  <include name="IDR_LAYERED_API_ELEMENTS_INTERNAL_REFLECTION_MJS" file="../renderer/core/script/resources/layered_api/elements/internal/reflection.mjs" type="BINDATA" skip_minify="true" compress="gzip"/>
+  <include name="IDR_LAYERED_API_ELEMENTS_SWITCH_FACE_UTILS_MJS" file="../renderer/core/script/resources/layered_api/elements/switch/face_utils.mjs" type="BINDATA" skip_minify="true" compress="gzip"/>
+  <include name="IDR_LAYERED_API_ELEMENTS_SWITCH_INDEX_MJS" file="../renderer/core/script/resources/layered_api/elements/switch/index.mjs" type="BINDATA" skip_minify="true" compress="gzip"/>
+  <include name="IDR_LAYERED_API_ELEMENTS_SWITCH_STYLE_MJS" file="../renderer/core/script/resources/layered_api/elements/switch/style.mjs" type="BINDATA" skip_minify="true" compress="gzip"/>
+  <include name="IDR_LAYERED_API_ELEMENTS_SWITCH_TRACK_MJS" file="../renderer/core/script/resources/layered_api/elements/switch/track.mjs" type="BINDATA" skip_minify="true" compress="gzip"/>
+  <include name="IDR_LAYERED_API_ELEMENTS_TOAST_INDEX_MJS" file="../renderer/core/script/resources/layered_api/elements/toast/index.mjs" type="BINDATA" skip_minify="true" compress="gzip"/>
+  <include name="IDR_LAYERED_API_ELEMENTS_VIRTUAL_SCROLLER_FIND_ELEMENT_MJS" file="../renderer/core/script/resources/layered_api/elements/virtual-scroller/find-element.mjs" type="BINDATA" skip_minify="true" compress="gzip"/>
+  <include name="IDR_LAYERED_API_ELEMENTS_VIRTUAL_SCROLLER_INDEX_MJS" file="../renderer/core/script/resources/layered_api/elements/virtual-scroller/index.mjs" type="BINDATA" skip_minify="true" compress="gzip"/>
+  <include name="IDR_LAYERED_API_ELEMENTS_VIRTUAL_SCROLLER_SETS_MJS" file="../renderer/core/script/resources/layered_api/elements/virtual-scroller/sets.mjs" type="BINDATA" skip_minify="true" compress="gzip"/>
+  <include name="IDR_LAYERED_API_ELEMENTS_VIRTUAL_SCROLLER_VISIBILITY_MANAGER_MJS" file="../renderer/core/script/resources/layered_api/elements/virtual-scroller/visibility-manager.mjs" type="BINDATA" skip_minify="true" compress="gzip"/>
   <include name="IDR_LAYERED_API_KV_STORAGE_ASYNC_ITERATOR_MJS" file="../renderer/core/script/resources/layered_api/kv-storage/async_iterator.mjs" type="BINDATA" skip_minify="true" compress="gzip"/>
   <include name="IDR_LAYERED_API_KV_STORAGE_IDB_UTILS_MJS" file="../renderer/core/script/resources/layered_api/kv-storage/idb_utils.mjs" type="BINDATA" skip_minify="true" compress="gzip"/>
   <include name="IDR_LAYERED_API_KV_STORAGE_INDEX_MJS" file="../renderer/core/script/resources/layered_api/kv-storage/index.mjs" type="BINDATA" skip_minify="true" compress="gzip"/>
-  <include name="IDR_LAYERED_API_VIRTUAL_SCROLLER_INDEX_MJS" file="../renderer/core/script/resources/layered_api/virtual-scroller/index.mjs" type="BINDATA" skip_minify="true" compress="gzip"/>
-  <include name="IDR_LAYERED_API_VIRTUAL_SCROLLER_ITEM_SOURCE_MJS" file="../renderer/core/script/resources/layered_api/virtual-scroller/item-source.mjs" type="BINDATA" skip_minify="true" compress="gzip"/>
-  <include name="IDR_LAYERED_API_VIRTUAL_SCROLLER_VIRTUAL_REPEATER_MJS" file="../renderer/core/script/resources/layered_api/virtual-scroller/virtual-repeater.mjs" type="BINDATA" skip_minify="true" compress="gzip"/>
-  <include name="IDR_LAYERED_API_VIRTUAL_SCROLLER_VIRTUAL_SCROLLER_MJS" file="../renderer/core/script/resources/layered_api/virtual-scroller/virtual-scroller.mjs" type="BINDATA" skip_minify="true" compress="gzip"/>
-  <include name="IDR_LAYERED_API_VIRTUAL_SCROLLER_LAYOUTS_LAYOUT_1D_BASE_MJS" file="../renderer/core/script/resources/layered_api/virtual-scroller/layouts/layout-1d-base.mjs" type="BINDATA" skip_minify="true" compress="gzip"/>
-  <include name="IDR_LAYERED_API_VIRTUAL_SCROLLER_LAYOUTS_LAYOUT_1D_GRID_MJS" file="../renderer/core/script/resources/layered_api/virtual-scroller/layouts/layout-1d-grid.mjs" type="BINDATA" skip_minify="true" compress="gzip"/>
-  <include name="IDR_LAYERED_API_VIRTUAL_SCROLLER_LAYOUTS_LAYOUT_1D_MJS" file="../renderer/core/script/resources/layered_api/virtual-scroller/layouts/layout-1d.mjs" type="BINDATA" skip_minify="true" compress="gzip"/>
 </grit-part>
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/virtual-scroller/README.chromium b/chromium/third_party/blink/renderer/core/script/resources/layered_api/virtual-scroller/README.chromium
deleted file mode 100644
index e8b4d5d0007..00000000000
--- a/chromium/third_party/blink/renderer/core/script/resources/layered_api/virtual-scroller/README.chromium
+++ /dev/null
@@ -1,12 +0,0 @@
-Name: virtual-scroller Layered API
-URL: https://github.com/valdrinkoshi/virtual-scroller
-Version: 58659cee10c5d9237821d5c475dac89720bd995d
-Security Critical: no
-
-Description:
-Temporarily, the files under this directory are authored by Chromium Authors
-on a github repository, and then imported to Chromium repository directly here,
-until a long-term Layered API development plan is settled.
-
-Local Modifications:
-None (except for renaming virtual-scroller-element.mjs to index.mjs)
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/virtual-scroller/index.mjs b/chromium/third_party/blink/renderer/core/script/resources/layered_api/virtual-scroller/index.mjs
deleted file mode 100644
index 8cdad8091f7..00000000000
--- a/chromium/third_party/blink/renderer/core/script/resources/layered_api/virtual-scroller/index.mjs
+++ /dev/null
@@ -1,213 +0,0 @@
-import {_item, _key, ItemSource} from './item-source.mjs';
-import {default as Layout1dGrid} from './layouts/layout-1d-grid.mjs';
-import {default as Layout1d} from './layouts/layout-1d.mjs';
-import {VirtualScroller} from './virtual-scroller.mjs';
-
-export {ItemSource};
-
-/** Properties */
-const _scroller = Symbol();
-const _createElement = Symbol();
-const _updateElement = Symbol();
-const _recycleElement = Symbol();
-const _nodePool = Symbol();
-const _rawItemSource = Symbol();
-const _itemSource = Symbol();
-const _elementSource = Symbol();
-const _firstConnected = Symbol();
-/** Functions */
-const _render = Symbol();
-
-export class VirtualScrollerElement extends HTMLElement {
-  constructor() {
-    super();
-    this[_scroller] = null;
-    // Default create/update/recycleElement.
-    this[_nodePool] = [];
-    let childTemplate = null;
-    this[_createElement] = () => {
-      if (this[_nodePool] && this[_nodePool].length) {
-        return this[_nodePool].pop();
-      }
-      if (!childTemplate) {
-        const template = this.querySelector('template');
-        childTemplate = template && template.content.firstElementChild ?
-            template.content.firstElementChild :
-            document.createElement('div');
-      }
-      return childTemplate.cloneNode(true);
-    };
-    this[_updateElement] = (element, item) => element.textContent =
-        item.toString();
-    this[_recycleElement] = (element) => this[_nodePool].push(element);
-
-    this[_itemSource] = this[_rawItemSource] = null;
-    this[_elementSource] = {};
-
-    this[_firstConnected] = false;
-  }
-
-  connectedCallback() {
-    if (!this[_firstConnected]) {
-      this.attachShadow({mode: 'open'}).innerHTML = `
-<style>
-  :host {
-    display: block;
-    position: relative;
-    contain: strict;
-    height: 150px;
-    overflow: auto;
-  }
-  :host([hidden]) {
-    display: none;
-  }
-  ::slotted(*) {
-    box-sizing: border-box;
-  }
-  :host([layout=vertical]) ::slotted(*) {
-    width: 100%;
-  }
-  :host([layout=horizontal]) ::slotted(*) {
-    height: 100%;
-  }
-</style>
-<slot></slot>`;
-      // Set default values.
-      if (!this.layout) {
-        this.layout = 'vertical';
-      }
-      // Enables rendering.
-      this[_firstConnected] = true;
-    }
-    this[_render]();
-  }
-
-  static get observedAttributes() {
-    return ['layout'];
-  }
-
-  attributeChangedCallback(name, oldVal, newVal) {
-    this[_render]();
-  }
-
-  get layout() {
-    return this.getAttribute('layout');
-  }
-  set layout(layout) {
-    this.setAttribute('layout', layout);
-  }
-
-  get itemSource() {
-    return this[_itemSource];
-  }
-  set itemSource(itemSource) {
-    // No Change.
-    if (this[_rawItemSource] === itemSource) {
-      return;
-    }
-    this[_rawItemSource] = itemSource;
-    this[_itemSource] = Array.isArray(itemSource) ?
-        ItemSource.fromArray(itemSource) :
-        itemSource;
-    this[_render]();
-  }
-
-  get createElement() {
-    return this[_createElement];
-  }
-  set createElement(fn) {
-    // Resets default recycling.
-    if (this[_nodePool]) {
-      this.recycleElement = null;
-    }
-    this[_createElement] = fn;
-    // Invalidate wrapped function.
-    this[_elementSource].createElement = null;
-    this[_render]();
-  }
-
-  get updateElement() {
-    return this[_updateElement];
-  }
-  set updateElement(fn) {
-    this[_updateElement] = fn;
-    // Invalidate wrapped function.
-    this[_elementSource].updateElement = null;
-    this[_render]();
-  }
-
-  get recycleElement() {
-    return this[_recycleElement];
-  }
-  set recycleElement(fn) {
-    // Marks default recycling changed.
-    this[_nodePool] = null;
-    this[_recycleElement] = fn;
-    // Invalidate wrapped function.
-    this[_elementSource].recycleElement = null;
-    this[_render]();
-  }
-
-  itemsChanged() {
-    if (this[_scroller]) {
-      // Render because length might have changed.
-      this[_render]();
-      // Request reset because items might have changed.
-      this[_scroller].requestReset();
-    }
-  }
-
-  scrollToIndex(index, { position = 'start' } = {}) {
-    if (this[_scroller]) {
-      this[_scroller].layout.scrollToIndex(index, position);
-    }
-  }
-
-  [_render]() {
-    // Wait first connected as scroller needs to measure
-    // sizes of container and children.
-    if (!this[_firstConnected] || !this.createElement) {
-      return;
-    }
-    if (!this[_scroller]) {
-      this[_scroller] =
-          new VirtualScroller({container: this, scrollTarget: this});
-    }
-    const scroller = this[_scroller];
-
-    const layoutAttr = this.layout;
-    const Layout = layoutAttr.endsWith('-grid') ? Layout1dGrid : Layout1d;
-    const direction =
-        layoutAttr.startsWith('horizontal') ? 'horizontal' : 'vertical';
-    const layout = scroller.layout instanceof Layout &&
-            scroller.layout.direction === direction ?
-        scroller.layout :
-        new Layout({direction});
-
-    let {createElement, updateElement, recycleElement} = this[_elementSource];
-    if (!createElement) {
-      createElement = this[_elementSource].createElement = (index) =>
-          this.createElement(this.itemSource[_item](index), index);
-    }
-    if (this.updateElement && !updateElement) {
-      updateElement = this[_elementSource].updateElement = (element, index) =>
-          this.updateElement(element, this.itemSource[_item](index), index);
-    }
-    if (this.recycleElement && !recycleElement) {
-      recycleElement = this[_elementSource].recycleElement = (element, index) =>
-          this.recycleElement(element, this.itemSource[_item](index), index);
-    }
-
-    const elementKey = this.itemSource ? this.itemSource[_key] : null;
-    const totalItems = this.itemSource ? this.itemSource.length : 0;
-    Object.assign(scroller, {
-      layout,
-      createElement,
-      updateElement,
-      recycleElement,
-      elementKey,
-      totalItems
-    });
-  }
-}
-customElements.define('virtual-scroller', VirtualScrollerElement);
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/virtual-scroller/item-source.mjs b/chromium/third_party/blink/renderer/core/script/resources/layered_api/virtual-scroller/item-source.mjs
deleted file mode 100644
index 255e97b245c..00000000000
--- a/chromium/third_party/blink/renderer/core/script/resources/layered_api/virtual-scroller/item-source.mjs
+++ /dev/null
@@ -1,47 +0,0 @@
-export const _getLength = Symbol();
-export const _item = Symbol();
-export const _key = Symbol();
-
-export class ItemSource {
-  constructor({getLength, item, key}) {
-    if (typeof getLength !== 'function') {
-      throw new TypeError('getLength option must be a function');
-    }
-    if (typeof item !== 'function') {
-      throw new TypeError('item option must be a function');
-    }
-    if (typeof key !== 'function') {
-      throw new TypeError('key option must be a function');
-    }
-
-    this[_getLength] = getLength;
-    this[_item] = item;
-    this[_key] = key;
-  }
-
-  static fromArray(array, key) {
-    if (!Array.isArray(array)) {
-      throw new TypeError('First argument to fromArray() must be an array');
-    }
-    if (typeof key !== 'function' && key !== undefined) {
-      throw new TypeError(
-          'Second argument to fromArray() must be a function or undefined');
-    }
-
-    return new this({
-      getLength() {
-        return array.length;
-      },
-      item(index) {
-        return array[index];
-      },
-      key(index) {
-        return key ? key(array[index], index) : array[index];
-      }
-    });
-  }
-
-  get length() {
-    return this[_getLength]();
-  }
-}
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/virtual-scroller/layouts/layout-1d-base.mjs b/chromium/third_party/blink/renderer/core/script/resources/layered_api/virtual-scroller/layouts/layout-1d-base.mjs
deleted file mode 100644
index 89a9a9e8106..00000000000
--- a/chromium/third_party/blink/renderer/core/script/resources/layered_api/virtual-scroller/layouts/layout-1d-base.mjs
+++ /dev/null
@@ -1,320 +0,0 @@
-export default class Layout extends EventTarget {
-  constructor(config) {
-    super();
-
-    this._physicalMin = 0;
-    this._physicalMax = 0;
-
-    this._first = -1;
-    this._last = -1;
-
-    this._latestCoords = {left: 0, top: 0};
-
-    this._itemSize = {width: 100, height: 100};
-    this._spacing = 0;
-
-    this._sizeDim = 'height';
-    this._secondarySizeDim = 'width';
-    this._positionDim = 'top';
-    this._secondaryPositionDim = 'left';
-    this._direction = 'vertical';
-
-    this._scrollPosition = 0;
-    this._scrollError = 0;
-    this._viewportSize = {width: 0, height: 0};
-    this._totalItems = 0;
-
-    this._scrollSize = 1;
-
-    this._overhang = 150;
-
-    this._pendingReflow = false;
-
-    this._scrollToIndex = -1;
-    this._scrollToAnchor = 0;
-
-    Object.assign(this, config);
-  }
-
-  // public properties
-
-  get totalItems() {
-    return this._totalItems;
-  }
-  set totalItems(num) {
-    if (num !== this._totalItems) {
-      this._totalItems = num;
-      this._maxIdx = num - 1;
-      this._scheduleReflow();
-    }
-  }
-
-  get direction() {
-    return this._direction;
-  }
-  set direction(dir) {
-    // Force it to be either horizontal or vertical.
-    dir = (dir === 'horizontal') ? dir : 'vertical';
-    if (dir !== this._direction) {
-      this._direction = dir;
-      this._sizeDim = (dir === 'horizontal') ? 'width' : 'height';
-      this._secondarySizeDim = (dir === 'horizontal') ? 'height' : 'width';
-      this._positionDim = (dir === 'horizontal') ? 'left' : 'top';
-      this._secondaryPositionDim = (dir === 'horizontal') ? 'top' : 'left';
-      this._scheduleReflow();
-    }
-  }
-
-  get itemSize() {
-    return this._itemSize;
-  }
-  set itemSize(dims) {
-    const {_itemDim1, _itemDim2} = this;
-    Object.assign(this._itemSize, dims);
-    if (_itemDim1 !== this._itemDim1 || _itemDim2 !== this._itemDim2) {
-      if (_itemDim2 !== this._itemDim2) {
-        this._itemDim2Changed();
-      } else {
-        this._scheduleReflow();
-      }
-    }
-  }
-
-  get spacing() {
-    return this._spacing;
-  }
-  set spacing(px) {
-    if (px !== this._spacing) {
-      this._spacing = px;
-      this._scheduleReflow();
-    }
-  }
-
-  get viewportSize() {
-    return this._viewportSize;
-  }
-  set viewportSize(dims) {
-    const {_viewDim1, _viewDim2} = this;
-    Object.assign(this._viewportSize, dims);
-    if (_viewDim2 !== this._viewDim2) {
-      this._viewDim2Changed();
-    } else if (_viewDim1 !== this._viewDim1) {
-      this._checkThresholds();
-    }
-  }
-
-  get viewportScroll() {
-    return this._latestCoords;
-  }
-  set viewportScroll(coords) {
-    Object.assign(this._latestCoords, coords);
-    const oldPos = this._scrollPosition;
-    this._scrollPosition = this._latestCoords[this._positionDim];
-    if (oldPos !== this._scrollPosition) {
-      this._scrollPositionChanged(oldPos, this._scrollPosition);
-    }
-    this._checkThresholds();
-  }
-
-  // private properties
-
-  get _delta() {
-    return this._itemDim1 + this._spacing;
-  }
-
-  get _itemDim1() {
-    return this._itemSize[this._sizeDim];
-  }
-
-  get _itemDim2() {
-    return this._itemSize[this._secondarySizeDim];
-  }
-
-  get _viewDim1() {
-    return this._viewportSize[this._sizeDim];
-  }
-
-  get _viewDim2() {
-    return this._viewportSize[this._secondarySizeDim];
-  }
-
-  get _num() {
-    if (this._first === -1 || this._last === -1) {
-      return 0;
-    }
-    return this._last - this._first + 1;
-  }
-
-  // public methods
-
-  reflowIfNeeded() {
-    if (this._pendingReflow) {
-      this._pendingReflow = false;
-      this._reflow();
-    }
-  }
-
-  scrollToIndex(index, position = 'start') {
-    if (!Number.isFinite(index))
-      return;
-    index = Math.min(this.totalItems, Math.max(0, index));
-    this._scrollToIndex = index;
-    if (position === 'nearest') {
-      position = index > this._first + this._num / 2 ? 'end' : 'start';
-    }
-    switch (position) {
-      case 'start':
-        this._scrollToAnchor = 0;
-        break;
-      case 'center':
-        this._scrollToAnchor = 0.5;
-        break;
-      case 'end':
-        this._scrollToAnchor = 1;
-        break;
-      default:
-        throw new TypeError(
-            'position must be one of: start, center, end, nearest');
-    }
-    this._scheduleReflow();
-    this.reflowIfNeeded();
-  }
-
-  ///
-
-  _scheduleReflow() {
-    this._pendingReflow = true;
-  }
-
-  _reflow() {
-    const {_first, _last, _scrollSize} = this;
-
-    this._updateScrollSize();
-    this._getActiveItems();
-    this._scrollIfNeeded();
-
-    if (this._scrollSize !== _scrollSize) {
-      this._emitScrollSize();
-    }
-
-    if (this._first === -1 && this._last === -1) {
-      this._emitRange();
-    } else if (
-        this._first !== _first || this._last !== _last ||
-        this._spacingChanged) {
-      this._emitRange();
-      this._emitChildPositions();
-    }
-    this._emitScrollError();
-  }
-
-  _updateScrollSize() {
-    // Ensure we have at least 1px - this allows getting at least 1 item to be
-    // rendered.
-    this._scrollSize = Math.max(1, this._totalItems * this._delta);
-  }
-
-  _checkThresholds() {
-    if (this._viewDim1 === 0 && this._num > 0) {
-      this._scheduleReflow();
-    } else {
-      const min = Math.max(0, this._scrollPosition - this._overhang);
-      const max = Math.min(
-          this._scrollSize,
-          this._scrollPosition + this._viewDim1 + this._overhang);
-      if (this._physicalMin > min || this._physicalMax < max) {
-        this._scheduleReflow();
-      }
-    }
-  }
-
-  _scrollIfNeeded() {
-    if (this._scrollToIndex === -1) {
-      return;
-    }
-    const index = this._scrollToIndex;
-    const anchor = this._scrollToAnchor;
-    const pos = this._getItemPosition(index)[this._positionDim];
-    const size = this._getItemSize(index)[this._sizeDim];
-
-    const curAnchorPos = this._scrollPosition + this._viewDim1 * anchor;
-    const newAnchorPos = pos + size * anchor;
-    // Ensure scroll position is an integer within scroll bounds.
-    const scrollPosition = Math.floor(Math.min(
-        this._scrollSize - this._viewDim1,
-        Math.max(0, this._scrollPosition - curAnchorPos + newAnchorPos)));
-    this._scrollError += this._scrollPosition - scrollPosition;
-    this._scrollPosition = scrollPosition;
-  }
-
-  _emitRange(inProps) {
-    const detail = Object.assign(
-        {
-          first: this._first,
-          last: this._last,
-          num: this._num,
-          stable: true,
-        },
-        inProps);
-    this.dispatchEvent(new CustomEvent('rangechange', {detail}));
-  }
-
-  _emitScrollSize() {
-    const detail = {
-      [this._sizeDim]: this._scrollSize,
-    };
-    this.dispatchEvent(new CustomEvent('scrollsizechange', {detail}));
-  }
-
-  _emitScrollError() {
-    if (this._scrollError) {
-      const detail = {
-        [this._positionDim]: this._scrollError,
-        [this._secondaryPositionDim]: 0,
-      };
-      this.dispatchEvent(new CustomEvent('scrollerrorchange', {detail}));
-      this._scrollError = 0;
-    }
-  }
-
-  _emitChildPositions() {
-    const detail = {};
-    for (let idx = this._first; idx <= this._last; idx++) {
-      detail[idx] = this._getItemPosition(idx);
-    }
-    this.dispatchEvent(new CustomEvent('itempositionchange', {detail}));
-  }
-
-  _itemDim2Changed() {
-    // Override
-  }
-
-  _viewDim2Changed() {
-    // Override
-  }
-
-  _scrollPositionChanged(oldPos, newPos) {
-    // When both values are bigger than the max scroll position, keep the
-    // current _scrollToIndexx, otherwise invalidate it.
-    const maxPos = this._scrollSize - this._viewDim1;
-    if (oldPos < maxPos || newPos < maxPos) {
-      this._scrollToIndex = -1;
-    }
-  }
-
-  _getActiveItems() {
-    // Override
-  }
-
-  _getItemPosition(idx) {
-    // Override.
-  }
-
-  _getItemSize(idx) {
-    // Override.
-    return {
-      [this._sizeDim]: this._itemDim1,
-      [this._secondarySizeDim]: this._itemDim2,
-    };
-  }
-}
\ No newline at end of file
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/virtual-scroller/layouts/layout-1d-grid.mjs b/chromium/third_party/blink/renderer/core/script/resources/layered_api/virtual-scroller/layouts/layout-1d-grid.mjs
deleted file mode 100644
index c9c00d021da..00000000000
--- a/chromium/third_party/blink/renderer/core/script/resources/layered_api/virtual-scroller/layouts/layout-1d-grid.mjs
+++ /dev/null
@@ -1,64 +0,0 @@
-import Layout1dBase from './layout-1d-base.mjs';
-
-export default class Layout extends Layout1dBase {
-  constructor(config) {
-    super(config);
-    this._rolumns = 1;
-  }
-
-  updateItemSizes(sizes) {
-    // Assume all items have the same size.
-    const size = Object.values(sizes)[0];
-    if (size) {
-      this.itemSize = size;
-    }
-  }
-
-  _viewDim2Changed() {
-    this._defineGrid();
-  }
-
-  _itemDim2Changed() {
-    this._defineGrid();
-  }
-
-  _getActiveItems() {
-    const min = Math.max(0, this._scrollPosition - this._overhang);
-    const max = Math.min(
-        this._scrollSize,
-        this._scrollPosition + this._viewDim1 + this._overhang);
-    const firstCow = Math.floor(min / this._delta);
-    const lastCow = Math.ceil(max / this._delta) - 1;
-
-    this._first = firstCow * this._rolumns;
-    this._last =
-        Math.min(((lastCow + 1) * this._rolumns) - 1, this._totalItems);
-    this._physicalMin = this._delta * firstCow;
-    this._physicalMax = this._delta * (lastCow + 1);
-  }
-
-  _getItemPosition(idx) {
-    return {
-      [this._positionDim]: Math.floor(idx / this._rolumns) * this._delta,
-          [this._secondaryPositionDim]: this._spacing +
-          ((idx % this._rolumns) * (this._spacing + this._itemDim2))
-    }
-  }
-
-
-  _defineGrid() {
-    const {_spacing} = this;
-    this._rolumns = Math.max(1, Math.floor(this._viewDim2 / this._itemDim2));
-    if (this._rolumns > 1) {
-      this._spacing = (this._viewDim2 % (this._rolumns * this._itemDim2)) /
-          (this._rolumns + 1);
-    }
-    this._spacingChanged = !(_spacing === this._spacing);
-    this._scheduleReflow();
-  }
-
-  _updateScrollSize() {
-    this._scrollSize =
-        Math.max(1, Math.ceil(this._totalItems / this._rolumns) * this._delta);
-  }
-}
\ No newline at end of file
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/virtual-scroller/layouts/layout-1d.mjs b/chromium/third_party/blink/renderer/core/script/resources/layered_api/virtual-scroller/layouts/layout-1d.mjs
deleted file mode 100644
index 6f5d181cb0e..00000000000
--- a/chromium/third_party/blink/renderer/core/script/resources/layered_api/virtual-scroller/layouts/layout-1d.mjs
+++ /dev/null
@@ -1,349 +0,0 @@
-import Layout1dBase from './layout-1d-base.mjs';
-
-export default class Layout extends Layout1dBase {
-  constructor(config) {
-    super(config);
-    this._physicalItems = new Map();
-    this._newPhysicalItems = new Map();
-
-    this._metrics = new Map();
-
-    this._anchorIdx = null;
-    this._anchorPos = null;
-    this._stable = true;
-
-    this._needsRemeasure = false;
-
-    this._nMeasured = 0;
-    this._tMeasured = 0;
-
-    this._estimate = true;
-  }
-
-  updateItemSizes(sizes) {
-    Object.keys(sizes).forEach((key) => {
-      const metrics = sizes[key], mi = this._getMetrics(key),
-            prevSize = mi[this._sizeDim];
-
-      // TODO(valdrin) Handle margin collapsing.
-      // https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Box_Model/Mastering_margin_collapsing
-      mi.width = metrics.width + (metrics.marginLeft || 0) +
-          (metrics.marginRight || 0);
-      mi.height = metrics.height + (metrics.marginTop || 0) +
-          (metrics.marginBottom || 0);
-
-      const size = mi[this._sizeDim];
-      const item = this._getPhysicalItem(Number(key));
-      if (item) {
-        let delta;
-
-        if (size !== undefined) {
-          item.size = size;
-          if (prevSize === undefined) {
-            delta = size;
-            this._nMeasured++;
-          } else {
-            delta = size - prevSize;
-          }
-        }
-        this._tMeasured = this._tMeasured + delta;
-      } else {
-        // console.debug(`Could not find physical item for key ${key}`);
-      }
-    });
-    if (!this._nMeasured) {
-      console.warn(`No items measured yet.`);
-    } else {
-      this._updateItemSize();
-      this._scheduleReflow();
-    }
-  }
-
-  _updateItemSize() {
-    // Keep integer values.
-    this._itemSize[this._sizeDim] =
-        Math.round(this._tMeasured / this._nMeasured);
-  }
-
-  //
-
-  _getMetrics(idx) {
-    return (this._metrics[idx] = this._metrics[idx] || {});
-  }
-
-  _getPhysicalItem(idx) {
-    return this._newPhysicalItems.get(idx) || this._physicalItems.get(idx);
-  }
-
-  _getSize(idx) {
-    const item = this._getPhysicalItem(idx);
-    return item && item.size;
-  }
-
-  _getPosition(idx) {
-    const item = this._physicalItems.get(idx);
-    return item ? item.pos : (idx * (this._delta)) + this._spacing;
-  }
-
-  _calculateAnchor(lower, upper) {
-    if (lower === 0) {
-      return 0;
-    }
-    if (upper > this._scrollSize - this._viewDim1) {
-      return this._maxIdx;
-    }
-    return Math.max(
-        0,
-        Math.min(
-            this._maxIdx, Math.floor(((lower + upper) / 2) / this._delta)));
-  }
-
-  _getAnchor(lower, upper) {
-    if (this._physicalItems.size === 0) {
-      return this._calculateAnchor(lower, upper);
-    }
-    if (this._first < 0) {
-      console.error('_getAnchor: negative _first');
-      return this._calculateAnchor(lower, upper);
-    }
-    if (this._last < 0) {
-      console.error('_getAnchor: negative _last');
-      return this._calculateAnchor(lower, upper);
-    }
-
-    const firstItem = this._getPhysicalItem(this._first),
-          lastItem = this._getPhysicalItem(this._last),
-          firstMin = firstItem.pos, firstMax = firstMin + firstItem.size,
-          lastMin = lastItem.pos, lastMax = lastMin + lastItem.size;
-
-    if (lastMax < lower) {
-      // Window is entirely past physical items, calculate new anchor
-      return this._calculateAnchor(lower, upper);
-    }
-    if (firstMin > upper) {
-      // Window is entirely before physical items, calculate new anchor
-      return this._calculateAnchor(lower, upper);
-    }
-    if (firstMin >= lower || firstMax >= lower) {
-      // First physical item overlaps window, choose it
-      return this._first;
-    }
-    if (lastMax <= upper || lastMin <= upper) {
-      // Last physical overlaps window, choose it
-      return this._last;
-    }
-    // Window contains a physical item, but not the first or last
-    let maxIdx = this._last, minIdx = this._first;
-
-    while (true) {
-      let candidateIdx = Math.round((maxIdx + minIdx) / 2),
-          candidate = this._physicalItems.get(candidateIdx),
-          cMin = candidate.pos, cMax = cMin + candidate.size;
-
-      if ((cMin >= lower && cMin <= upper) ||
-          (cMax >= lower && cMax <= upper)) {
-        return candidateIdx;
-      } else if (cMax < lower) {
-        minIdx = candidateIdx + 1;
-      } else if (cMin > upper) {
-        maxIdx = candidateIdx - 1;
-      }
-    }
-  }
-
-  _getActiveItems() {
-    if (this._viewDim1 === 0 || this._totalItems === 0) {
-      this._clearItems();
-    } else {
-      const upper = Math.min(
-          this._scrollSize,
-          this._scrollPosition + this._viewDim1 + this._overhang),
-            lower = Math.max(0, upper - this._viewDim1 - (2 * this._overhang));
-
-      this._getItems(lower, upper);
-    }
-  }
-
-  _clearItems() {
-    this._first = -1;
-    this._last = -1;
-    this._physicalMin = 0;
-    this._physicalMax = 0;
-    const items = this._newPhysicalItems;
-    this._newPhysicalItems = this._physicalItems;
-    this._newPhysicalItems.clear();
-    this._physicalItems = items;
-    this._stable = true;
-  }
-
-  _getItems(lower, upper) {
-    const items = this._newPhysicalItems;
-
-    // The anchorIdx is the anchor around which we reflow.
-    // It is designed to allow jumping to any point of the scroll size.
-    // We choose it once and stick with it until stable. first and last are
-    // deduced around it.
-    if (this._anchorIdx === null || this._anchorPos === null) {
-      this._anchorIdx = this._getAnchor(lower, upper);
-      this._anchorPos = this._getPosition(this._anchorIdx);
-    }
-
-    let anchorSize = this._getSize(this._anchorIdx);
-    if (anchorSize === undefined) {
-      anchorSize = this._itemDim1;
-    }
-
-    // Anchor might be outside bounds, so prefer correcting the error and keep
-    // that anchorIdx.
-    let anchorErr = 0;
-
-    if (this._anchorPos + anchorSize + this._spacing < lower) {
-      anchorErr = lower - (this._anchorPos + anchorSize + this._spacing);
-    }
-
-    if (this._anchorPos > upper) {
-      anchorErr = upper - this._anchorPos;
-    }
-
-    if (anchorErr) {
-      this._scrollPosition -= anchorErr;
-      lower -= anchorErr;
-      upper -= anchorErr;
-      this._scrollError += anchorErr;
-    }
-
-    items.set(this._anchorIdx, {pos: this._anchorPos, size: anchorSize});
-
-    this._first = (this._last = this._anchorIdx);
-    this._physicalMin = (this._physicalMax = this._anchorPos);
-
-    this._stable = true;
-
-    while (this._physicalMin > lower && this._first > 0) {
-      let size = this._getSize(--this._first);
-      if (size === undefined) {
-        this._stable = false;
-        size = this._itemDim1;
-      }
-      const pos = (this._physicalMin -= size + this._spacing);
-      items.set(this._first, {pos, size});
-      if (this._stable === false && this._estimate === false) {
-        break;
-      }
-    }
-
-    while (this._physicalMax < upper && this._last < this._totalItems) {
-      let size = this._getSize(this._last);
-      if (size === undefined) {
-        this._stable = false;
-        size = this._itemDim1;
-      }
-      items.set(this._last++, {pos: this._physicalMax, size});
-      if (this._stable === false && this._estimate === false) {
-        break;
-      } else {
-        this._physicalMax += size + this._spacing;
-      }
-    }
-
-    this._last--;
-
-    // This handles the cases where we were relying on estimated sizes.
-    const extentErr = this._calculateError();
-    if (extentErr) {
-      this._physicalMin -= extentErr;
-      this._physicalMax -= extentErr;
-      this._anchorPos -= extentErr;
-      this._scrollPosition -= extentErr;
-      items.forEach(item => item.pos -= extentErr);
-      this._scrollError += extentErr;
-    }
-
-    if (this._stable) {
-      this._newPhysicalItems = this._physicalItems;
-      this._newPhysicalItems.clear();
-      this._physicalItems = items;
-    }
-  }
-
-  _calculateError() {
-    if (this._first === 0) {
-      return this._physicalMin;
-    } else if (this._physicalMin <= 0) {
-      return this._physicalMin - (this._first * this._delta);
-    } else if (this._last === this._maxIdx) {
-      return this._physicalMax - this._scrollSize;
-    } else if (this._physicalMax >= this._scrollSize) {
-      return (
-          (this._physicalMax - this._scrollSize) +
-          ((this._maxIdx - this._last) * this._delta));
-    }
-    return 0;
-  }
-
-  _updateScrollSize() {
-    // Reuse previously calculated physical max, as it might be
-    // higher than the estimated size.
-    super._updateScrollSize();
-    this._scrollSize = Math.max(this._physicalMax, this._scrollSize);
-  }
-
-  // TODO: Can this be made to inherit from base, with proper hooks?
-  _reflow() {
-    const {_first, _last, _scrollSize} = this;
-
-    this._updateScrollSize();
-    this._getActiveItems();
-    this._scrollIfNeeded();
-
-    if (this._scrollSize !== _scrollSize) {
-      this._emitScrollSize();
-    }
-
-    this._emitRange();
-    if (this._first === -1 && this._last === -1) {
-      this._resetReflowState();
-    } else if (
-        this._first !== _first || this._last !== _last ||
-        this._needsRemeasure) {
-      this._emitChildPositions();
-      this._emitScrollError();
-    } else {
-      this._emitChildPositions();
-      this._emitScrollError();
-      this._resetReflowState();
-    }
-  }
-
-  _resetReflowState() {
-    this._anchorIdx = null;
-    this._anchorPos = null;
-    this._stable = true;
-  }
-
-  _getItemPosition(idx) {
-    return {
-      [this._positionDim]: this._getPosition(idx),
-          [this._secondaryPositionDim]: 0
-    }
-  }
-
-  _getItemSize(idx) {
-    return {
-      [this._sizeDim]: this._getSize(idx) || this._itemDim1,
-      [this._secondarySizeDim]: this._itemDim2,
-    };
-  }
-
-  _viewDim2Changed() {
-    this._needsRemeasure = true;
-    this._scheduleReflow();
-  }
-
-  _emitRange() {
-    const remeasure = this._needsRemeasure;
-    const stable = this._stable;
-    this._needsRemeasure = false;
-    super._emitRange({remeasure, stable});
-  }
-}
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/virtual-scroller/virtual-repeater.mjs b/chromium/third_party/blink/renderer/core/script/resources/layered_api/virtual-scroller/virtual-repeater.mjs
deleted file mode 100644
index 3d3cb6aa7c1..00000000000
--- a/chromium/third_party/blink/renderer/core/script/resources/layered_api/virtual-scroller/virtual-repeater.mjs
+++ /dev/null
@@ -1,531 +0,0 @@
-export const Repeats = Superclass => class extends Superclass {
-  constructor(config) {
-    super();
-
-    this._createElementFn = null;
-    this._updateElementFn = null;
-    this._recycleElementFn = null;
-    this._elementKeyFn = null;
-
-    this._measureCallback = null;
-
-    this._totalItems = 0;
-    // Consider renaming this. firstVisibleIndex?
-    this._first = 0;
-    // Consider renaming this. count? visibleElements?
-    this._num = Infinity;
-
-    this.__incremental = false;
-
-    // used only internally..
-    // legacy from 1st approach to preact integration
-    this._manageDom = true;
-    // used to check if it is more perf if you don't care of dom order?
-    this._maintainDomOrder = true;
-
-    this._last = 0;
-    this._prevFirst = 0;
-    this._prevLast = 0;
-
-    this._needsReset = false;
-    this._needsRemeasure = false;
-    this._pendingRender = null;
-
-    // Contains child nodes in the rendered order.
-    this._ordered = [];
-    // this._pool = [];
-    this._active = new Map();
-    this._prevActive = new Map();
-    // Both used for recycling purposes.
-    this._keyToChild = new Map();
-    this._childToKey = new WeakMap();
-    // Used to keep track of measures by index.
-    this._indexToMeasure = {};
-    // Used to debounce _measureChildren calls.
-    this._measuringId = -1;
-
-    if (config) {
-      Object.assign(this, config);
-    }
-  }
-
-  // API
-
-  get container() {
-    return this._container;
-  }
-  set container(container) {
-    if (container === this._container) {
-      return;
-    }
-    if (this._container) {
-      // Remove children from old container.
-      this._ordered.forEach((child) => this._removeChild(child));
-    }
-
-    this._container = container;
-
-    if (container) {
-      // Insert children in new container.
-      this._ordered.forEach((child) => this._insertBefore(child, null));
-    } else {
-      this._ordered.length = 0;
-      this._active.clear();
-      this._prevActive.clear();
-    }
-    this.requestReset();
-  }
-
-  get createElement() {
-    return this._createElementFn;
-  }
-  set createElement(fn) {
-    if (fn !== this._createElementFn) {
-      this._createElementFn = fn;
-      this._keyToChild.clear();
-      this.requestReset();
-    }
-  }
-
-  get updateElement() {
-    return this._updateElementFn;
-  }
-  set updateElement(fn) {
-    if (fn !== this._updateElementFn) {
-      this._updateElementFn = fn;
-      this.requestReset();
-    }
-  }
-
-  get recycleElement() {
-    return this._recycleElementFn;
-  }
-  set recycleElement(fn) {
-    if (fn !== this._recycleElementFn) {
-      this._recycleElementFn = fn;
-      this.requestReset();
-    }
-  }
-
-  get elementKey() {
-    return this._elementKeyFn;
-  }
-  set elementKey(fn) {
-    if (fn !== this._elementKeyFn) {
-      this._elementKeyFn = fn;
-      this._keyToChild.clear();
-      this.requestReset();
-    }
-  }
-
-  get first() {
-    return this._first;
-  }
-
-  set first(idx) {
-    if (typeof idx === 'number') {
-      const newFirst = Math.max(0, Math.min(idx, this._totalItems - this._num));
-      if (newFirst !== this._first) {
-        this._first = newFirst;
-        this._scheduleRender();
-      }
-    }
-  }
-
-  get num() {
-    return this._num;
-  }
-
-  set num(n) {
-    if (typeof n === 'number') {
-      if (n !== this._num) {
-        this._num = n;
-        this.first = this._first;
-        this._scheduleRender();
-      }
-    }
-  }
-
-  get totalItems() {
-    return this._totalItems;
-  }
-
-  set totalItems(num) {
-    // TODO(valdrin) should we check if it is a finite number?
-    // Technically, Infinity would break Layout, not VirtualRepeater.
-    if (typeof num === 'number' && num !== this._totalItems) {
-      this._totalItems = num;
-      this.first = this._first;
-      this.requestReset();
-    }
-  }
-
-  get _incremental() {
-    return this.__incremental;
-  }
-
-  set _incremental(inc) {
-    if (inc !== this.__incremental) {
-      this.__incremental = inc;
-      this._scheduleRender();
-    }
-  }
-
-  requestReset() {
-    this._needsReset = true;
-    this._scheduleRender();
-  }
-
-  requestRemeasure() {
-    this._needsRemeasure = true;
-    this._scheduleRender();
-  }
-
-  // Core functionality
-
-  /**
-   * @protected
-   */
-  _shouldRender() {
-    return Boolean(this.container && this.createElement);
-  }
-
-  /**
-   * @private
-   */
-  _scheduleRender() {
-    if (!this._pendingRender) {
-      this._pendingRender = requestAnimationFrame(() => {
-        this._pendingRender = null;
-        if (this._shouldRender()) {
-          this._render();
-        }
-      });
-    }
-  }
-
-  /**
-   * Returns those children that are about to be displayed and that
-   * require to be positioned. If reset or remeasure has been triggered,
-   * all children are returned.
-   * @return {{indices:Array<number>,children:Array<Element>}}
-   * @private
-   */
-  get _toMeasure() {
-    return this._ordered.reduce((toMeasure, c, i) => {
-      const idx = this._first + i;
-      if (this._needsReset || this._needsRemeasure || idx < this._prevFirst ||
-          idx > this._prevLast) {
-        toMeasure.indices.push(idx);
-        toMeasure.children.push(c);
-      }
-      return toMeasure;
-    }, {indices: [], children: []});
-  }
-
-  /**
-   * Measures each child bounds and builds a map of index/bounds to be passed to
-   * the `_measureCallback`
-   * @private
-   */
-  _measureChildren({indices, children}) {
-    let pm = children.map(
-        (c, i) => this._indexToMeasure[indices[i]] || this._measureChild(c));
-    const mm = /** @type {{ number: { width: number, height: number } }} */
-        (pm.reduce((out, cur, i) => {
-          out[indices[i]] = this._indexToMeasure[indices[i]] = cur;
-          return out;
-        }, {}));
-    this._measureCallback(mm);
-  }
-
-  /**
-   * @protected
-   */
-  _render() {
-    const rangeChanged =
-        this._first !== this._prevFirst || this._num !== this._prevNum;
-    // Create/update/recycle DOM.
-    if (rangeChanged || this._needsReset) {
-      this._last =
-          this._first + Math.min(this._num, this._totalItems - this._first) - 1;
-      if (this._num || this._prevNum) {
-        if (this._needsReset) {
-          this._reset(this._first, this._last);
-        } else {
-          this._discardHead();
-          this._discardTail();
-          this._addHead();
-          this._addTail();
-        }
-      }
-    }
-    if (this._needsRemeasure || this._needsReset) {
-      this._indexToMeasure = {};
-    }
-    // Retrieve DOM to be measured.
-    // Do it right before cleanup and reset of properties.
-    const shouldMeasure = this._num > 0 && this._measureCallback &&
-        (rangeChanged || this._needsRemeasure || this._needsReset);
-    const toMeasure = shouldMeasure ? this._toMeasure : null;
-
-    // Cleanup.
-    if (!this._incremental) {
-      this._prevActive.forEach((idx, child) => this._unassignChild(child, idx));
-      this._prevActive.clear();
-    }
-    // Reset internal properties.
-    this._prevFirst = this._first;
-    this._prevLast = this._last;
-    this._prevNum = this._num;
-    this._needsReset = false;
-    this._needsRemeasure = false;
-
-    // Notify render completed.
-    this._didRender();
-    // Measure DOM.
-    if (toMeasure) {
-      this._measureChildren(toMeasure);
-    }
-  }
-
-  /**
-   * Invoked after DOM is updated, and before it gets measured.
-   * @protected
-   */
-  _didRender() {
-  }
-
-  /**
-   * @private
-   */
-  _discardHead() {
-    const o = this._ordered;
-    for (let idx = this._prevFirst; o.length && idx < this._first; idx++) {
-      this._unassignChild(o.shift(), idx);
-    }
-  }
-
-  /**
-   * @private
-   */
-  _discardTail() {
-    const o = this._ordered;
-    for (let idx = this._prevLast; o.length && idx > this._last; idx--) {
-      this._unassignChild(o.pop(), idx);
-    }
-  }
-
-  /**
-   * @private
-   */
-  _addHead() {
-    const start = this._first;
-    const end = Math.min(this._last, this._prevFirst - 1);
-    for (let idx = end; idx >= start; idx--) {
-      const child = this._assignChild(idx);
-      if (this._manageDom) {
-        if (this._maintainDomOrder || !this._childIsAttached(child)) {
-          this._insertBefore(child, this._firstChild);
-        }
-      }
-      if (this.updateElement) {
-        this.updateElement(child, idx);
-      }
-      this._ordered.unshift(child);
-    }
-  }
-
-  /**
-   * @private
-   */
-  _addTail() {
-    const start = Math.max(this._first, this._prevLast + 1);
-    const end = this._last;
-    for (let idx = start; idx <= end; idx++) {
-      const child = this._assignChild(idx);
-      if (this._manageDom) {
-        if (this._maintainDomOrder || !this._childIsAttached(child)) {
-          this._insertBefore(child, null);
-        }
-      }
-      if (this.updateElement) {
-        this.updateElement(child, idx);
-      }
-      this._ordered.push(child);
-    }
-  }
-
-  /**
-   * @param {number} first
-   * @param {number} last
-   * @private
-   */
-  _reset(first, last) {
-    const len = last - first + 1;
-    // Explain why swap prevActive with active - affects _assignChild.
-    const prevActive = this._active;
-    this._active = this._prevActive;
-    this._prevActive = prevActive;
-    let currentMarker = this._manageDom && this._firstChild;
-    this._ordered.length = 0;
-    for (let n = 0; n < len; n++) {
-      const idx = first + n;
-      const child = this._assignChild(idx);
-      this._ordered.push(child);
-      if (this._manageDom) {
-        if (currentMarker && this._maintainDomOrder) {
-          if (currentMarker === this._node(child)) {
-            currentMarker = this._nextSibling(child);
-          } else {
-            this._insertBefore(child, currentMarker);
-          }
-        } else if (!this._childIsAttached(child)) {
-          this._insertBefore(child, null);
-        }
-      }
-      if (this.updateElement) {
-        this.updateElement(child, idx);
-      }
-    }
-  }
-
-  /**
-   * @param {number} idx
-   * @private
-   */
-  _assignChild(idx) {
-    const key = this.elementKey ? this.elementKey(idx) : idx;
-    let child;
-    if (child = this._keyToChild.get(key)) {
-      this._prevActive.delete(child);
-    } else {
-      child = this.createElement(idx);
-      this._keyToChild.set(key, child);
-      this._childToKey.set(child, key);
-    }
-    this._showChild(child);
-    this._active.set(child, idx);
-    return child;
-  }
-
-  /**
-   * @param {*} child
-   * @param {number} idx
-   * @private
-   */
-  _unassignChild(child, idx) {
-    this._hideChild(child);
-    if (this._incremental) {
-      this._active.delete(child);
-      this._prevActive.set(child, idx);
-    } else {
-      const key = this._childToKey.get(child);
-      this._childToKey.delete(child);
-      this._keyToChild.delete(key);
-      this._active.delete(child);
-      if (this.recycleElement) {
-        this.recycleElement(child, idx);
-      } else if (this._node(child).parentNode) {
-        this._removeChild(child);
-      }
-    }
-  }
-
-  // TODO: Is this the right name?
-  /**
-   * @private
-   */
-  get _firstChild() {
-    return this._ordered.length && this._childIsAttached(this._ordered[0]) ?
-        this._node(this._ordered[0]) :
-        null;
-  }
-
-  // Overridable abstractions for child manipulation
-  /**
-   * @protected
-   */
-  _node(child) {
-    return child;
-  }
-  /**
-   * @protected
-   */
-  _nextSibling(child) {
-    return child.nextSibling;
-  }
-  /**
-   * @protected
-   */
-  _insertBefore(child, referenceNode) {
-    this._container.insertBefore(child, referenceNode);
-  }
-  /**
-   * @protected
-   */
-  _childIsAttached(child) {
-    const node = this._node(child);
-    return node && node.parentNode === this._container;
-  }
-  /**
-   * @protected
-   */
-  _hideChild(child) {
-    if (child.style) {
-      child.style.display = 'none';
-    }
-  }
-  /**
-   * @protected
-   */
-  _showChild(child) {
-    if (child.style) {
-      child.style.display = null;
-    }
-  }
-
-  /**
-   *
-   * @param {!Element} child
-   * @return {{width: number, height: number, marginTop: number, marginBottom: number, marginLeft: number, marginRight: number}} childMeasures
-   * @protected
-   */
-  _measureChild(child) {
-    // offsetWidth doesn't take transforms in consideration,
-    // so we use getBoundingClientRect which does.
-    const {width, height} = child.getBoundingClientRect();
-    // console.debug(`_measureChild #${this._container.id} > #${
-    //     child.id}: height: ${height}px`);
-    return Object.assign({width, height}, getMargins(child));
-  }
-
-  /**
-   * Remove child.
-   * Override to control child removal.
-   *
-   * @param {*} child
-   * @protected
-   */
-  _removeChild(child) {
-    child.parentNode.removeChild(child);
-  }
-}
-
-function getMargins(el) {
-  const style = window.getComputedStyle(el);
-  // console.log(el.id, style.position);
-  return {
-    marginLeft: getMarginValue(style.marginLeft),
-    marginRight: getMarginValue(style.marginRight),
-    marginTop: getMarginValue(style.marginTop),
-    marginBottom: getMarginValue(style.marginBottom),
-  };
-}
-
-function getMarginValue(value) {
-  value = value ? parseFloat(value) : NaN;
-  return value !== value ? 0 : value;
-}
-
-export const VirtualRepeater = Repeats(class {});
\ No newline at end of file
diff --git a/chromium/third_party/blink/renderer/core/script/resources/layered_api/virtual-scroller/virtual-scroller.mjs b/chromium/third_party/blink/renderer/core/script/resources/layered_api/virtual-scroller/virtual-scroller.mjs
deleted file mode 100644
index 049501e6ec9..00000000000
--- a/chromium/third_party/blink/renderer/core/script/resources/layered_api/virtual-scroller/virtual-scroller.mjs
+++ /dev/null
@@ -1,444 +0,0 @@
-import {Repeats} from './virtual-repeater.mjs';
-
-export class RangeChangeEvent extends Event {
-  constructor(type, init) {
-    super(type, init);
-    this._first = Math.floor(init.first || 0);
-    this._last = Math.floor(init.last || 0);
-  }
-  get first() {
-    return this._first;
-  }
-  get last() {
-    return this._last;
-  }
-}
-
-export const RepeatsAndScrolls = Superclass => class extends Repeats
-(Superclass) {
-  constructor(config) {
-    super();
-    this._num = 0;
-    this._first = -1;
-    this._last = -1;
-    this._prevFirst = -1;
-    this._prevLast = -1;
-
-    this._needsUpdateView = false;
-    this._containerElement = null;
-    this._layout = null;
-    this._scrollTarget = null;
-    // Keep track of original inline style of the container,
-    // so it can be restored when container is changed.
-    this._containerInlineStyle = null;
-    // A sentinel element that sizes the container when
-    // it is a scrolling element.
-    this._sizer = null;
-    // Layout provides these values, we set them on _render().
-    this._scrollSize = null;
-    this._scrollErr = null;
-    this._childrenPos = null;
-
-    this._containerSize = null;
-    this._containerRO = new ResizeObserver(
-        (entries) => this._containerSizeChanged(entries[0].contentRect));
-
-    this._skipNextChildrenSizeChanged = false;
-    this._childrenRO =
-        new ResizeObserver((entries) => this._childrenSizeChanged(entries));
-
-    if (config) {
-      Object.assign(this, config);
-    }
-  }
-
-  get container() {
-    return this._container;
-  }
-  set container(container) {
-    super.container = container;
-
-    const oldEl = this._containerElement;
-    // Consider document fragments as shadowRoots.
-    const newEl =
-        (container && container.nodeType === Node.DOCUMENT_FRAGMENT_NODE) ?
-        container.host :
-        container;
-    if (oldEl === newEl) {
-      return;
-    }
-
-    this._containerRO.disconnect();
-    this._containerSize = null;
-
-    if (oldEl) {
-      if (this._containerInlineStyle) {
-        oldEl.setAttribute('style', this._containerInlineStyle);
-      } else {
-        oldEl.removeAttribute('style');
-      }
-      this._containerInlineStyle = null;
-      if (oldEl === this._scrollTarget) {
-        oldEl.removeEventListener('scroll', this, {passive: true});
-        this._sizer && this._sizer.remove();
-      }
-    } else {
-      // First time container was setup, add listeners only now.
-      addEventListener('scroll', this, {passive: true});
-    }
-
-    this._containerElement = newEl;
-
-    if (newEl) {
-      this._containerInlineStyle = newEl.getAttribute('style') || null;
-      if (newEl === this._scrollTarget) {
-        this._sizer = this._sizer || this._createContainerSizer();
-        this._container.prepend(this._sizer);
-      }
-      this._scheduleUpdateView();
-      this._containerRO.observe(newEl);
-    }
-  }
-
-  get layout() {
-    return this._layout;
-  }
-  set layout(layout) {
-    if (layout === this._layout) {
-      return;
-    }
-
-    if (this._layout) {
-      this._measureCallback = null;
-      this._layout.removeEventListener('scrollsizechange', this);
-      this._layout.removeEventListener('scrollerrorchange', this);
-      this._layout.removeEventListener('itempositionchange', this);
-      this._layout.removeEventListener('rangechange', this);
-      // Reset container size so layout can get correct viewport size.
-      if (this._containerElement) {
-        this._sizeContainer();
-      }
-    }
-
-    this._layout = layout;
-
-    if (this._layout) {
-      if (typeof this._layout.updateItemSizes === 'function') {
-        this._measureCallback = this._layout.updateItemSizes.bind(this._layout);
-        this.requestRemeasure();
-      }
-      this._layout.addEventListener('scrollsizechange', this);
-      this._layout.addEventListener('scrollerrorchange', this);
-      this._layout.addEventListener('itempositionchange', this);
-      this._layout.addEventListener('rangechange', this);
-      this._scheduleUpdateView();
-    }
-  }
-
-  /**
-   * The element that generates scroll events and defines the container
-   * viewport. The value `null` (default) corresponds to `window` as scroll
-   * target.
-   * @type {Element|null}
-   */
-  get scrollTarget() {
-    return this._scrollTarget;
-  }
-  /**
-   * @param {Element|null} target
-   */
-  set scrollTarget(target) {
-    // Consider window as null.
-    if (target === window) {
-      target = null;
-    }
-    if (this._scrollTarget === target) {
-      return;
-    }
-    if (this._scrollTarget) {
-      this._scrollTarget.removeEventListener('scroll', this, {passive: true});
-      if (this._sizer && this._scrollTarget === this._containerElement) {
-        this._sizer.remove();
-      }
-    }
-
-    this._scrollTarget = target;
-
-    if (target) {
-      target.addEventListener('scroll', this, {passive: true});
-      if (target === this._containerElement) {
-        this._sizer = this._sizer || this._createContainerSizer();
-        this._container.prepend(this._sizer);
-      }
-    }
-  }
-
-  /**
-   * @protected
-   */
-  _render() {
-    // console.time(`render ${this._containerElement.localName}#${
-    //     this._containerElement.id}`);
-
-    this._childrenRO.disconnect();
-
-    // Update layout properties before rendering to have correct
-    // first, num, scroll size, children positions.
-    this._layout.totalItems = this.totalItems;
-    if (this._needsUpdateView) {
-      this._needsUpdateView = false;
-      this._updateView();
-    }
-    this._layout.reflowIfNeeded();
-    // Keep rendering until there is no more scheduled renders.
-    while (true) {
-      if (this._pendingRender) {
-        cancelAnimationFrame(this._pendingRender);
-        this._pendingRender = null;
-      }
-      // Update scroll size and correct scroll error before rendering.
-      this._sizeContainer(this._scrollSize);
-      if (this._scrollErr) {
-        // This triggers a 'scroll' event (async) which triggers another
-        // _updateView().
-        this._correctScrollError(this._scrollErr);
-        this._scrollErr = null;
-      }
-      // Position children (_didRender()), and provide their measures to layout.
-      super._render();
-      this._layout.reflowIfNeeded();
-      // If layout reflow did not provoke another render, we're done.
-      if (!this._pendingRender) {
-        break;
-      }
-    }
-    // We want to skip the first ResizeObserver callback call as we already
-    // measured the children.
-    this._skipNextChildrenSizeChanged = true;
-    this._kids.forEach(child => this._childrenRO.observe(child));
-
-    // console.timeEnd(`render ${this._containerElement.localName}#${
-    //     this._containerElement.id}`);
-  }
-
-  /**
-   * Position children before they get measured.
-   * Measuring will force relayout, so by positioning
-   * them first, we reduce computations.
-   * @protected
-   */
-  _didRender() {
-    if (this._childrenPos) {
-      this._positionChildren(this._childrenPos);
-      this._childrenPos = null;
-    }
-  }
-
-  /**
-   * @param {!Event} event
-   * @private
-   */
-  handleEvent(event) {
-    switch (event.type) {
-      case 'scroll':
-        if (!this._scrollTarget || event.target === this._scrollTarget) {
-          this._scheduleUpdateView();
-        }
-        break;
-      case 'scrollsizechange':
-        this._scrollSize = event.detail;
-        this._scheduleRender();
-        break;
-      case 'scrollerrorchange':
-        this._scrollErr = event.detail;
-        this._scheduleRender();
-        break;
-      case 'itempositionchange':
-        this._childrenPos = event.detail;
-        this._scheduleRender();
-        break;
-      case 'rangechange':
-        this._adjustRange(event.detail);
-        break;
-      default:
-        console.warn('event not handled', event);
-    }
-  }
-  /**
-   * @return {!Element}
-   * @private
-   */
-  _createContainerSizer() {
-    const sizer = document.createElement('div');
-    // When the scrollHeight is large, the height
-    // of this element might be ignored.
-    // Setting content and font-size ensures the element
-    // has a size.
-    Object.assign(sizer.style, {
-      position: 'absolute',
-      margin: '-2px 0 0 0',
-      padding: 0,
-      visibility: 'hidden',
-      fontSize: '2px',
-    });
-    sizer.innerHTML = '&nbsp;';
-    return sizer;
-  }
-
-  // Rename _ordered to _kids?
-  /**
-   * @protected
-   */
-  get _kids() {
-    return this._ordered;
-  }
-  /**
-   * @private
-   */
-  _scheduleUpdateView() {
-    this._needsUpdateView = true;
-    this._scheduleRender();
-  }
-  /**
-   * @private
-   */
-  _updateView() {
-    let width, height, top, left;
-    if (this._scrollTarget === this._containerElement) {
-      width = this._containerSize.width;
-      height = this._containerSize.height;
-      left = this._containerElement.scrollLeft;
-      top = this._containerElement.scrollTop;
-    } else {
-      const containerBounds = this._containerElement.getBoundingClientRect();
-      const scrollBounds = this._scrollTarget ?
-          this._scrollTarget.getBoundingClientRect() :
-          {top: 0, left: 0, width: innerWidth, height: innerHeight};
-      const scrollerWidth = scrollBounds.width;
-      const scrollerHeight = scrollBounds.height;
-      const xMin = Math.max(
-          0, Math.min(scrollerWidth, containerBounds.left - scrollBounds.left));
-      const yMin = Math.max(
-          0, Math.min(scrollerHeight, containerBounds.top - scrollBounds.top));
-      const xMax = this._layout.direction === 'vertical' ?
-          Math.max(
-              0,
-              Math.min(
-                  scrollerWidth, containerBounds.right - scrollBounds.left)) :
-          scrollerWidth;
-      const yMax = this._layout.direction === 'vertical' ?
-          scrollerHeight :
-          Math.max(
-              0,
-              Math.min(
-                  scrollerHeight, containerBounds.bottom - scrollBounds.top));
-      width = xMax - xMin;
-      height = yMax - yMin;
-      left = Math.max(0, -(containerBounds.x - scrollBounds.left));
-      top = Math.max(0, -(containerBounds.y - scrollBounds.top));
-    }
-    this._layout.viewportSize = {width, height};
-    this._layout.viewportScroll = {top, left};
-  }
-  /**
-   * @private
-   */
-  _sizeContainer(size) {
-    if (this._scrollTarget === this._containerElement) {
-      const left = size && size.width ? size.width - 1 : 0;
-      const top = size && size.height ? size.height - 1 : 0;
-      this._sizer.style.transform = `translate(${left}px, ${top}px)`;
-    } else {
-      const style = this._containerElement.style;
-      style.minWidth = size && size.width ? size.width + 'px' : null;
-      style.minHeight = size && size.height ? size.height + 'px' : null;
-    }
-  }
-  /**
-   * @private
-   */
-  _positionChildren(pos) {
-    const kids = this._kids;
-    Object.keys(pos).forEach(key => {
-      const idx = key - this._first;
-      const child = kids[idx];
-      if (child) {
-        const {top, left} = pos[key];
-        // console.debug(`_positionChild #${this._container.id} >
-        // #${child.id}: top ${top}`);
-        child.style.position = 'absolute';
-        child.style.transform = `translate(${left}px, ${top}px)`;
-      }
-    });
-  }
-  /**
-   * @private
-   */
-  _adjustRange(range) {
-    this.num = range.num;
-    this.first = range.first;
-    this._incremental = !(range.stable);
-    if (range.remeasure) {
-      this.requestRemeasure();
-    } else if (range.stable) {
-      this._notifyStable();
-    }
-  }
-  /**
-   * @protected
-   */
-  _shouldRender() {
-    if (!super._shouldRender() || !this._layout) {
-      return false;
-    }
-    // NOTE: we're about to render, but the ResizeObserver didn't execute yet.
-    // Since we want to keep rAF timing, we compute _containerSize now.
-    // Would be nice to have a way to flush ResizeObservers
-    if (this._containerSize === null) {
-      const {width, height} = this._containerElement.getBoundingClientRect();
-      this._containerSize = {width, height};
-    }
-    return this._containerSize.width > 0 || this._containerSize.height > 0;
-  }
-  /**
-   * @private
-   */
-  _correctScrollError(err) {
-    if (this._scrollTarget) {
-      this._scrollTarget.scrollTop -= err.top;
-      this._scrollTarget.scrollLeft -= err.left;
-    } else {
-      window.scroll(window.scrollX - err.left, window.scrollY - err.top);
-    }
-  }
-  /**
-   * @protected
-   */
-  _notifyStable() {
-    const {first, num} = this;
-    const last = first + num - 1;
-    this._container.dispatchEvent(
-        new RangeChangeEvent('rangechange', {first, last}));
-  }
-  /**
-   * @private
-   */
-  _containerSizeChanged(size) {
-    const {width, height} = size;
-    this._containerSize = {width, height};
-    // console.debug('container changed size', this._containerSize);
-    this._scheduleUpdateView();
-  }
-  /**
-   * @private
-   */
-  _childrenSizeChanged() {
-    if (this._skipNextChildrenSizeChanged) {
-      this._skipNextChildrenSizeChanged = false;
-    } else {
-      this.requestRemeasure();
-    }
-  }
-};
-
-export const VirtualScroller = RepeatsAndScrolls(class {});
diff --git a/chromium/third_party/blink/renderer/core/script/script.h b/chromium/third_party/blink/renderer/core/script/script.h
index 2e99f96cb9c..d7951dc1f0a 100644
--- a/chromium/third_party/blink/renderer/core/script/script.h
+++ b/chromium/third_party/blink/renderer/core/script/script.h
@@ -21,7 +21,7 @@ class WorkerGlobalScope;
 // https://html.spec.whatwg.org/C/#concept-script
 class CORE_EXPORT Script : public GarbageCollectedFinalized<Script> {
  public:
-  virtual void Trace(blink::Visitor* visitor) {}
+  virtual void Trace(Visitor* visitor) {}
 
   virtual ~Script() {}
 
diff --git a/chromium/third_party/blink/renderer/core/script/script_loader.cc b/chromium/third_party/blink/renderer/core/script/script_loader.cc
index 41d5609b5f2..4666d857aed 100644
--- a/chromium/third_party/blink/renderer/core/script/script_loader.cc
+++ b/chromium/third_party/blink/renderer/core/script/script_loader.cc
@@ -33,7 +33,6 @@
 #include "third_party/blink/renderer/core/dom/text.h"
 #include "third_party/blink/renderer/core/frame/csp/content_security_policy.h"
 #include "third_party/blink/renderer/core/frame/local_frame.h"
-#include "third_party/blink/renderer/core/frame/use_counter.h"
 #include "third_party/blink/renderer/core/html/imports/html_import.h"
 #include "third_party/blink/renderer/core/html/parser/html_parser_idioms.h"
 #include "third_party/blink/renderer/core/html_names.h"
@@ -52,7 +51,8 @@
 #include "third_party/blink/renderer/core/script/script_runner.h"
 #include "third_party/blink/renderer/core/svg_names.h"
 #include "third_party/blink/renderer/platform/bindings/parkable_string.h"
-#include "third_party/blink/renderer/platform/histogram.h"
+#include "third_party/blink/renderer/platform/instrumentation/histogram.h"
+#include "third_party/blink/renderer/platform/instrumentation/use_counter.h"
 #include "third_party/blink/renderer/platform/loader/fetch/fetch_client_settings_object_snapshot.h"
 #include "third_party/blink/renderer/platform/loader/fetch/fetch_parameters.h"
 #include "third_party/blink/renderer/platform/loader/fetch/resource_fetcher.h"
@@ -71,7 +71,8 @@ ScriptLoader::ScriptLoader(ScriptElementBase* element,
                            bool already_started)
     : element_(element),
       will_be_parser_executed_(false),
-      will_execute_when_document_finished_parsing_(false) {
+      will_execute_when_document_finished_parsing_(false),
+      force_deferred_(false) {
   // <spec href="https://html.spec.whatwg.org/C/#already-started">... The
   // cloning steps for script elements must set the "already started" flag on
   // the copy if it is set on the element being cloned.</spec>
@@ -97,7 +98,7 @@ ScriptLoader::ScriptLoader(ScriptElementBase* element,
 
 ScriptLoader::~ScriptLoader() {}
 
-void ScriptLoader::Trace(blink::Visitor* visitor) {
+void ScriptLoader::Trace(Visitor* visitor) {
   visitor->Trace(element_);
   visitor->Trace(pending_script_);
   visitor->Trace(prepared_pending_script_);
@@ -279,17 +280,17 @@ bool ScriptLoader::BlockForNoModule(mojom::ScriptType script_type,
 //     https://html.spec.whatwg.org/C/#prepare-a-script
 //   - Step 6 of obtaining a preloaded module script
 //     https://html.spec.whatwg.org/C/#link-type-modulepreload.
-network::mojom::FetchCredentialsMode ScriptLoader::ModuleScriptCredentialsMode(
+network::mojom::CredentialsMode ScriptLoader::ModuleScriptCredentialsMode(
     CrossOriginAttributeValue cross_origin) {
   switch (cross_origin) {
     case kCrossOriginAttributeNotSet:
     case kCrossOriginAttributeAnonymous:
-      return network::mojom::FetchCredentialsMode::kSameOrigin;
+      return network::mojom::CredentialsMode::kSameOrigin;
     case kCrossOriginAttributeUseCredentials:
-      return network::mojom::FetchCredentialsMode::kInclude;
+      return network::mojom::CredentialsMode::kInclude;
   }
   NOTREACHED();
-  return network::mojom::FetchCredentialsMode::kOmit;
+  return network::mojom::CredentialsMode::kOmit;
 }
 
 // https://github.com/WICG/feature-policy/issues/135
@@ -449,7 +450,7 @@ bool ScriptLoader::PrepareScript(const TextPosition& script_start_position,
 
   // <spec step="17">Let module script credentials mode be the module script
   // credentials mode for the element's crossorigin content attribute.</spec>
-  network::mojom::FetchCredentialsMode credentials_mode =
+  network::mojom::CredentialsMode credentials_mode =
       ModuleScriptCredentialsMode(cross_origin);
 
   // <spec step="18">Let cryptographic nonce be the element's
@@ -583,7 +584,7 @@ bool ScriptLoader::PrepareScript(const TextPosition& script_start_position,
 
       // <spec step="24.6.B">"module"
       //
-      // Fetch a module script graph given url, settings object, "script", and
+      // Fetch an external module script graph given url, settings object, and
       // options.</spec>
       Modulator* modulator = Modulator::From(
           ToScriptStateForMainWorld(context_document->GetFrame()));
@@ -623,7 +624,7 @@ bool ScriptLoader::PrepareScript(const TextPosition& script_start_position,
 
     // <spec step="25.2">Switch on the script's type:</spec>
     switch (GetScriptType()) {
-      // <spec step="25.2.A">"classic"</spec>
+        // <spec step="25.2.A">"classic"</spec>
       case mojom::ScriptType::kClassic: {
         // <spec step="25.2.A.1">Let script be the result of creating a classic
         // script using source text, settings object, base URL, and
@@ -650,28 +651,38 @@ bool ScriptLoader::PrepareScript(const TextPosition& script_start_position,
         break;
       }
 
-      // <spec step="25.2.B">"module"</spec>
+        // <spec step="25.2.B">"module"</spec>
       case mojom::ScriptType::kModule: {
-        // <spec step="25.2.B.1">Let script be the result of creating a module
-        // script using source text, settings object, base URL, and
-        // options.</spec>
+        // <spec step="25.2.B.1">Fetch an inline module script graph, given
+        // source text, base URL, settings object, and options. When this
+        // asynchronously completes, set the script's script to the result. At
+        // that time, the script is ready.</spec>
+        //
+        // <specdef label="fetch-an-inline-module-script-graph"
+        // href="https://html.spec.whatwg.org/C/#fetch-an-inline-module-script-graph">
         const KURL& source_url = element_document.Url();
         Modulator* modulator = Modulator::From(
             ToScriptStateForMainWorld(context_document->GetFrame()));
+
+        // <spec label="fetch-an-inline-module-script-graph" step="1">Let script
+        // be the result of creating a JavaScript module script using source
+        // text, settings object, base URL, and options.</spec>
         ModuleScript* module_script = JSModuleScript::Create(
             ParkableString(element_->TextFromChildren().Impl()), nullptr,
             ScriptSourceLocationType::kInline, modulator, source_url, base_url,
             options, position);
 
-        // <spec step="25.2.B.2">If this returns null, set the script's script
-        // to null and return; the script is ready.</spec>
+        // <spec label="fetch-an-inline-module-script-graph" step="2">If script
+        // is null, asynchronously complete this algorithm with null, and abort
+        // these steps.</spec>
         if (!module_script)
           return false;
 
-        // <spec step="25.2.B.3">Fetch the descendants of and instantiate
-        // script, given settings object and the destination "script". When this
-        // asynchronously completes, set the script's script to the result. At
-        // that time, the script is ready.</spec>
+        // <spec label="fetch-an-inline-module-script-graph" step="4">Fetch the
+        // descendants of and instantiate script, given settings object, the
+        // destination "script", and visited set. When this asynchronously
+        // completes with final result, asynchronously complete this algorithm
+        // with final result.</spec>
         auto* module_tree_client =
             MakeGarbageCollected<ModulePendingScriptTreeClient>();
         modulator->FetchDescendantsForInlineScript(
@@ -718,6 +729,25 @@ bool ScriptLoader::PrepareScript(const TextPosition& script_start_position,
     return true;
   }
 
+  // Check for external script that should be force deferred.
+  if (GetScriptType() == mojom::ScriptType::kClassic &&
+      element_->HasSourceAttribute() &&
+      context_document->GetFrame()->ShouldForceDeferScript() &&
+      context_document->IsHTMLDocument() && parser_inserted_ &&
+      !element_->AsyncAttributeValue()) {
+    // In terms of ScriptLoader flags, force deferred scripts behave like
+    // parser-blocking scripts, except that |force_deferred_| is set.
+    // The caller of PrepareScript()
+    // - Force-defers such scripts if the caller supports force-defer
+    //   (i.e., HTMLParserScriptRunner); or
+    // - Ignores the |force_deferred_| flag and handles such scripts as
+    //   parser-blocking scripts (e.g., XMLParserScriptRunner).
+    force_deferred_ = true;
+    will_be_parser_executed_ = true;
+
+    return true;
+  }
+
   // <spec step="26.B">If the script's type is "classic", and the element has a
   // src attribute, and the element has been flagged as "parser-inserted", and
   // the element does not have an async attribute ...</spec>
@@ -793,6 +823,14 @@ bool ScriptLoader::PrepareScript(const TextPosition& script_start_position,
   DCHECK_EQ(GetScriptType(), mojom::ScriptType::kClassic);
   DCHECK(!is_external_script_);
 
+  // Check for inline script that should be force deferred.
+  if (context_document->GetFrame()->ShouldForceDeferScript() &&
+      context_document->IsHTMLDocument() && parser_inserted_) {
+    force_deferred_ = true;
+    will_be_parser_executed_ = true;
+    return true;
+  }
+
   // <spec step="26.E">If the element does not have a src attribute, and the
   // element has been flagged as "parser-inserted", and either the parser that
   // created the script is an XML parser or it's an HTML parser whose script
@@ -861,7 +899,7 @@ void ScriptLoader::FetchModuleScriptTree(
     const ScriptFetchOptions& options) {
   // <spec step="24.6.B">"module"
   //
-  // Fetch a module script graph given url, settings object, "script", and
+  // Fetch an external module script graph given url, settings object, and
   // options.</spec>
   auto* module_tree_client =
       MakeGarbageCollected<ModulePendingScriptTreeClient>();
@@ -880,23 +918,6 @@ PendingScript* ScriptLoader::TakePendingScript(
       EnumerationHistogram, scheduling_type_histogram,
       ("Blink.Script.SchedulingType", kLastScriptSchedulingType + 1));
   scheduling_type_histogram.Count(static_cast<int>(scheduling_type));
-
-  switch (scheduling_type) {
-    case ScriptSchedulingType::kAsync:
-    case ScriptSchedulingType::kInOrder:
-      // As ClassicPendingScript keeps a reference to ScriptResource,
-      // the ScriptResource is anyway kept alive until evaluation,
-      // and can be garbage-collected after that (together with
-      // ClassicPendingScript).
-      resource_keep_alive_ = nullptr;
-      break;
-
-    default:
-      // ScriptResource is kept alive by resource_keep_alive_
-      // until ScriptLoader is garbage collected.
-      break;
-  }
-
   PendingScript* pending_script = prepared_pending_script_;
   prepared_pending_script_ = nullptr;
   pending_script->SetSchedulingType(scheduling_type);
@@ -908,6 +929,19 @@ void ScriptLoader::PendingScriptFinished(PendingScript* pending_script) {
   DCHECK_EQ(pending_script_, pending_script);
   DCHECK_EQ(pending_script_->GetScriptType(), GetScriptType());
   DCHECK(pending_script->IsControlledByScriptRunner());
+  DCHECK(pending_script_->GetSchedulingType() == ScriptSchedulingType::kAsync ||
+         pending_script_->GetSchedulingType() ==
+             ScriptSchedulingType::kInOrder);
+  // Historically we clear |resource_keep_alive_| when the scheduling type is
+  // kAsync or kInOrder (crbug.com/778799). But if the script resource was
+  // served via signed exchange, the script may not be in the HTTPCache,
+  // therefore will need to be refetched over network if it's evicted from the
+  // memory cache not be in the HTTPCache. So we keep |resource_keep_alive_| to
+  // keep the resource in the memory cache.
+  if (resource_keep_alive_ &&
+      !resource_keep_alive_->GetResponse().IsSignedExchangeInnerResponse()) {
+    resource_keep_alive_ = nullptr;
+  }
 
   Document* context_document = element_->GetDocument().ContextDocument();
   if (!context_document) {
diff --git a/chromium/third_party/blink/renderer/core/script/script_loader.h b/chromium/third_party/blink/renderer/core/script/script_loader.h
index ae9e7b85a7a..0ac49da3bc0 100644
--- a/chromium/third_party/blink/renderer/core/script/script_loader.h
+++ b/chromium/third_party/blink/renderer/core/script/script_loader.h
@@ -56,7 +56,7 @@ class CORE_EXPORT ScriptLoader final
  public:
   ScriptLoader(ScriptElementBase*, bool created_by_parser, bool is_evaluated);
   ~ScriptLoader() override;
-  void Trace(blink::Visitor*) override;
+  void Trace(Visitor*) override;
   const char* NameInHeapSnapshot() const override { return "ScriptLoader"; }
 
   enum LegacyTypeSupport {
@@ -78,7 +78,7 @@ class CORE_EXPORT ScriptLoader final
 
   static bool BlockForNoModule(mojom::ScriptType, bool nomodule);
 
-  static network::mojom::FetchCredentialsMode ModuleScriptCredentialsMode(
+  static network::mojom::CredentialsMode ModuleScriptCredentialsMode(
       CrossOriginAttributeValue);
 
   // https://html.spec.whatwg.org/C/#prepare-a-script
@@ -96,6 +96,7 @@ class CORE_EXPORT ScriptLoader final
   bool WillExecuteWhenDocumentFinishedParsing() const {
     return will_execute_when_document_finished_parsing_;
   }
+  bool IsForceDeferred() const { return force_deferred_; }
   bool IsParserInserted() const { return parser_inserted_; }
   bool AlreadyStarted() const { return already_started_; }
   bool IsNonBlocking() const { return non_blocking_; }
@@ -145,33 +146,27 @@ class CORE_EXPORT ScriptLoader final
   // https://html.spec.whatwg.org/C/#script-processing-model
   // "A script element has several associated pieces of state.":
 
-  // <spec
-  // href="https://html.spec.whatwg.org/C/#already-started">
-  // ... Initially, script elements must have this flag unset ...</spec>
+  // <spec href="https://html.spec.whatwg.org/C/#already-started">... Initially,
+  // script elements must have this flag unset ...</spec>
   bool already_started_ = false;
 
-  // <spec
-  // href="https://html.spec.whatwg.org/C/#parser-inserted">
-  // ... Initially, script elements must have this flag unset. ...</spec>
+  // <spec href="https://html.spec.whatwg.org/C/#parser-inserted">... Initially,
+  // script elements must have this flag unset. ...</spec>
   bool parser_inserted_ = false;
 
-  // <spec
-  // href="https://html.spec.whatwg.org/C/#non-blocking">
-  // ... Initially, script elements must have this flag set. ...</spec>
+  // <spec href="https://html.spec.whatwg.org/C/#non-blocking">... Initially,
+  // script elements must have this flag set. ...</spec>
   bool non_blocking_ = true;
 
-  // <spec
-  // href="https://html.spec.whatwg.org/C/#ready-to-be-parser-executed">
+  // <spec href="https://html.spec.whatwg.org/C/#ready-to-be-parser-executed">
   // ... Initially, script elements must have this flag unset ...</spec>
   bool ready_to_be_parser_executed_ = false;
 
-  // <spec
-  // href="https://html.spec.whatwg.org/C/#concept-script-type">
-  // ... It is determined when the script is prepared, ...</spec>
+  // <spec href="https://html.spec.whatwg.org/C/#concept-script-type">... It is
+  // determined when the script is prepared, ...</spec>
   mojom::ScriptType script_type_ = mojom::ScriptType::kClassic;
 
-  // <spec
-  // href="https://html.spec.whatwg.org/C/#concept-script-external">
+  // <spec href="https://html.spec.whatwg.org/C/#concept-script-external">
   // ... It is determined when the script is prepared, ...</spec>
   bool is_external_script_ = false;
 
@@ -180,6 +175,9 @@ class CORE_EXPORT ScriptLoader final
 
   bool will_execute_when_document_finished_parsing_;
 
+  // The script will be force deferred (https://crbug.com/976061).
+  bool force_deferred_;
+
   // A PendingScript is first created in PrepareScript() and stored in
   // |prepared_pending_script_|.
   // Later, TakePendingScript() is called, and its caller holds a reference
diff --git a/chromium/third_party/blink/renderer/core/script/script_runner.cc b/chromium/third_party/blink/renderer/core/script/script_runner.cc
index 6e76a6417ec..c3e12f4ab8f 100644
--- a/chromium/third_party/blink/renderer/core/script/script_runner.cc
+++ b/chromium/third_party/blink/renderer/core/script/script_runner.cc
@@ -256,7 +256,7 @@ void ScriptRunner::ExecuteTask() {
 #endif
 }
 
-void ScriptRunner::Trace(blink::Visitor* visitor) {
+void ScriptRunner::Trace(Visitor* visitor) {
   visitor->Trace(document_);
   visitor->Trace(pending_in_order_scripts_);
   visitor->Trace(pending_async_scripts_);
diff --git a/chromium/third_party/blink/renderer/core/script/script_runner.h b/chromium/third_party/blink/renderer/core/script/script_runner.h
index 54ad3d801f9..75b69989ca9 100644
--- a/chromium/third_party/blink/renderer/core/script/script_runner.h
+++ b/chromium/third_party/blink/renderer/core/script/script_runner.h
@@ -58,7 +58,7 @@ class CORE_EXPORT ScriptRunner final
 
   static void MovePendingScript(Document&, Document&, ScriptLoader*);
 
-  void Trace(blink::Visitor*);
+  void Trace(Visitor*);
   const char* NameInHeapSnapshot() const override { return "ScriptRunner"; }
 
  private:
diff --git a/chromium/third_party/blink/renderer/core/script/script_scheduling_type.h b/chromium/third_party/blink/renderer/core/script/script_scheduling_type.h
index 928143ec895..744f0af5e93 100644
--- a/chromium/third_party/blink/renderer/core/script/script_scheduling_type.h
+++ b/chromium/third_party/blink/renderer/core/script/script_scheduling_type.h
@@ -62,7 +62,14 @@ enum class ScriptSchedulingType {
   kAsync,
 
   // Inline <script> executed immediately within prepare-a-script.
-  kImmediate
+  kImmediate,
+
+  // Force deferred scripts controlled by HTMLParserScriptRunner.
+  // These are otherwise parser-blocking scripts that are being forced to
+  // execute after parsing completes (due to a ForceDeferScriptIntervention).
+  //
+  // Spec: not yet spec'ed. https://crbug.com/976061
+  kForceDefer
 };
 
 static const int kLastScriptSchedulingType =
diff --git a/chromium/third_party/blink/renderer/core/script/value_wrapper_synthetic_module_script.cc b/chromium/third_party/blink/renderer/core/script/value_wrapper_synthetic_module_script.cc
new file mode 100644
index 00000000000..8ee3c96acf6
--- /dev/null
+++ b/chromium/third_party/blink/renderer/core/script/value_wrapper_synthetic_module_script.cc
@@ -0,0 +1,153 @@
+// Copyright 2019 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "third_party/blink/renderer/core/script/value_wrapper_synthetic_module_script.h"
+
+#include "third_party/blink/public/platform/web_vector.h"
+#include "third_party/blink/renderer/bindings/core/v8/v8_binding_for_core.h"
+#include "third_party/blink/renderer/core/loader/modulescript/module_script_creation_params.h"
+#include "third_party/blink/renderer/core/script/modulator.h"
+#include "third_party/blink/renderer/core/script/module_record_resolver.h"
+#include "third_party/blink/renderer/platform/weborigin/kurl.h"
+#include "third_party/blink/renderer/platform/wtf/text/text_position.h"
+#include "v8/include/v8.h"
+
+namespace blink {
+
+ValueWrapperSyntheticModuleScript*
+ValueWrapperSyntheticModuleScript::CreateJSONWrapperSyntheticModuleScript(
+    const base::Optional<ModuleScriptCreationParams>& params,
+    Modulator* settings_object,
+    const ScriptFetchOptions options_) {
+  DCHECK(settings_object->HasValidContext());
+  ScriptState::Scope scope(settings_object->GetScriptState());
+  v8::Local<v8::Context> context =
+      settings_object->GetScriptState()->GetContext();
+  v8::Isolate* isolate = context->GetIsolate();
+  v8::TryCatch try_catch(isolate);
+  v8::Local<v8::String> original_json =
+      V8String(isolate, params->GetSourceText().ToString());
+  v8::Local<v8::Value> parsed_json;
+  ExceptionState exception_state(isolate, ExceptionState::kExecutionContext,
+                                 "ModuleScriptLoader",
+                                 "CreateJSONWrapperSyntheticModuleScript");
+  // Step 1. "Let script be a new module script that this algorithm will
+  // subsequently initialize."
+  // [spec text]
+  // Step 2. "Set script's settings object to settings."
+  // [spec text]
+  // Step 3. "Set script's base URL and fetch options to null."
+  // [spec text]
+  // Step 4. "Set script's parse error and error to rethrow to null."
+  // [spec text]
+  // Step 5. "Let json be ? Call(%JSONParse%, undefined, « source »).
+  // If this throws an exception, set script's parse error to that exception,
+  // and return script."
+  // [spec text]
+  if (!v8::JSON::Parse(context, original_json).ToLocal(&parsed_json)) {
+    DCHECK(try_catch.HasCaught());
+    exception_state.RethrowV8Exception(try_catch.Exception());
+    v8::Local<v8::Value> error = exception_state.GetException();
+    exception_state.ClearException();
+    return ValueWrapperSyntheticModuleScript::CreateWithError(
+        parsed_json, settings_object, params->GetResponseUrl(),
+        params->GetResponseUrl(), options_, error);
+  } else {
+    return ValueWrapperSyntheticModuleScript::CreateWithDefaultExport(
+        parsed_json, settings_object, params->GetResponseUrl(),
+        params->GetResponseUrl(), options_);
+  }
+}
+
+ValueWrapperSyntheticModuleScript*
+ValueWrapperSyntheticModuleScript::CreateWithDefaultExport(
+    v8::Local<v8::Value> value,
+    Modulator* settings_object,
+    const KURL& source_url,
+    const KURL& base_url,
+    const ScriptFetchOptions& fetch_options,
+    const TextPosition& start_position) {
+  v8::Isolate* isolate = settings_object->GetScriptState()->GetIsolate();
+  std::vector<v8::Local<v8::String>> export_names{V8String(isolate, "default")};
+  v8::Local<v8::Module> v8_synthetic_module = v8::Module::CreateSyntheticModule(
+      isolate, V8String(isolate, source_url.GetString()), export_names,
+      ValueWrapperSyntheticModuleScript::EvaluationSteps);
+  // Step 6. "Set script's record to the result of creating a synthetic module
+  // record with a default export of json with settings."
+  // [spec text]
+  ModuleRecord record = ModuleRecord(isolate, v8_synthetic_module, source_url);
+
+  ValueWrapperSyntheticModuleScript* value_wrapper_module_script =
+      MakeGarbageCollected<ValueWrapperSyntheticModuleScript>(
+          settings_object, record, source_url, base_url, fetch_options, value,
+          start_position);
+  settings_object->GetModuleRecordResolver()->RegisterModuleScript(
+      value_wrapper_module_script);
+  // Step 7. "Return script."
+  // [spec text]
+  return value_wrapper_module_script;
+}
+
+ValueWrapperSyntheticModuleScript*
+ValueWrapperSyntheticModuleScript::CreateWithError(
+    v8::Local<v8::Value> value,
+    Modulator* settings_object,
+    const KURL& source_url,
+    const KURL& base_url,
+    const ScriptFetchOptions& fetch_options,
+    v8::Local<v8::Value> error,
+    const TextPosition& start_position) {
+  ValueWrapperSyntheticModuleScript* value_wrapper_module_script =
+      MakeGarbageCollected<ValueWrapperSyntheticModuleScript>(
+          settings_object, ModuleRecord(), source_url, base_url, fetch_options,
+          value, start_position);
+  settings_object->GetModuleRecordResolver()->RegisterModuleScript(
+      value_wrapper_module_script);
+  value_wrapper_module_script->SetParseErrorAndClearRecord(
+      ScriptValue(settings_object->GetScriptState(), error));
+  // Step 7. "Return script."
+  // [spec text]
+  return value_wrapper_module_script;
+}
+
+ValueWrapperSyntheticModuleScript::ValueWrapperSyntheticModuleScript(
+    Modulator* settings_object,
+    ModuleRecord record,
+    const KURL& source_url,
+    const KURL& base_url,
+    const ScriptFetchOptions& fetch_options,
+    v8::Local<v8::Value> value,
+    const TextPosition& start_position)
+    : ModuleScript(settings_object,
+                   record,
+                   source_url,
+                   base_url,
+                   fetch_options),
+      export_value_(v8::Isolate::GetCurrent(), value) {}
+
+// TODO(sasebree) Implement this method
+v8::MaybeLocal<v8::Value> ValueWrapperSyntheticModuleScript::EvaluationSteps(
+    v8::Local<v8::Context> context,
+    v8::Local<v8::Module> module) {
+  NOTREACHED();
+  return v8::MaybeLocal<v8::Value>();
+}
+
+String ValueWrapperSyntheticModuleScript::InlineSourceTextForCSP() const {
+  // We don't construct a ValueWrapperSyntheticModuleScript with the original
+  // source, but instead construct it from the originally parsed
+  // text. If a need arises for the original module source to be used later,
+  // ValueWrapperSyntheticModuleScript will need to be modified such that its
+  // constructor takes this source text as an additional parameter and stashes
+  // it on the ValueWrapperSyntheticModuleScript.
+  NOTREACHED();
+  return "";
+}
+
+void ValueWrapperSyntheticModuleScript::Trace(Visitor* visitor) {
+  visitor->Trace(export_value_);
+  ModuleScript::Trace(visitor);
+}
+
+}  // namespace blink
\ No newline at end of file
diff --git a/chromium/third_party/blink/renderer/core/script/value_wrapper_synthetic_module_script.h b/chromium/third_party/blink/renderer/core/script/value_wrapper_synthetic_module_script.h
new file mode 100644
index 00000000000..ae19c095cd9
--- /dev/null
+++ b/chromium/third_party/blink/renderer/core/script/value_wrapper_synthetic_module_script.h
@@ -0,0 +1,78 @@
+// Copyright 2019 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef THIRD_PARTY_BLINK_RENDERER_CORE_SCRIPT_VALUE_WRAPPER_SYNTHETIC_MODULE_SCRIPT_H_
+#define THIRD_PARTY_BLINK_RENDERER_CORE_SCRIPT_VALUE_WRAPPER_SYNTHETIC_MODULE_SCRIPT_H_
+
+#include "third_party/blink/renderer/core/core_export.h"
+#include "third_party/blink/renderer/core/script/module_script.h"
+
+namespace WTF {
+class TextPosition;
+}  // namespace WTF
+
+namespace blink {
+
+class KURL;
+class Modulator;
+class ModuleScriptCreationParams;
+
+// ValueWrapperSyntheticModuleScript is a module script
+// (https://html.spec.whatwg.org/C/#module-script) that default-exports a single
+// v8::Value, for example JSON Module Script:
+// https://html.spec.whatwg.org/multipage/webappapis.html#json-module-script
+class CORE_EXPORT ValueWrapperSyntheticModuleScript final
+    : public ModuleScript {
+ public:
+  static ValueWrapperSyntheticModuleScript*
+  CreateJSONWrapperSyntheticModuleScript(
+      const base::Optional<ModuleScriptCreationParams>& params,
+      Modulator* settings_object,
+      const ScriptFetchOptions options_);
+
+  static ValueWrapperSyntheticModuleScript* CreateWithDefaultExport(
+      v8::Local<v8::Value> value,
+      Modulator* settings_object,
+      const KURL& source_url,
+      const KURL& base_url,
+      const ScriptFetchOptions& fetch_options,
+      const TextPosition& start_position = TextPosition::MinimumPosition());
+
+  static ValueWrapperSyntheticModuleScript* CreateWithError(
+      v8::Local<v8::Value> value,
+      Modulator* settings_object,
+      const KURL& source_url,
+      const KURL& base_url,
+      const ScriptFetchOptions& fetch_options,
+      v8::Local<v8::Value> error,
+      const TextPosition& start_position = TextPosition::MinimumPosition());
+
+  ValueWrapperSyntheticModuleScript(Modulator* settings_object,
+                                    ModuleRecord record,
+                                    const KURL& source_url,
+                                    const KURL& base_url,
+                                    const ScriptFetchOptions& fetch_options,
+                                    v8::Local<v8::Value> value,
+                                    const TextPosition& start_position);
+
+  // <specdef
+  // href="https://heycam.github.io/webidl/#synthetic-module-record">
+  // An abstract operation that will be performed upon evaluation of the module,
+  // taking the Synthetic Module Record as its sole argument. These will usually
+  // set up the exported values, by using SetSyntheticModuleExport. They must
+  // not modify [[ExportNames]]. They may return an abrupt completion.
+  static v8::MaybeLocal<v8::Value> EvaluationSteps(
+      v8::Local<v8::Context> context,
+      v8::Local<v8::Module> module);
+
+  String InlineSourceTextForCSP() const override;
+  void Trace(blink::Visitor* visitor) override;
+
+ private:
+  TraceWrapperV8Reference<v8::Value> export_value_;
+};
+
+}  // namespace blink
+
+#endif  // THIRD_PARTY_BLINK_RENDERER_CORE_SCRIPT_VALUE_WRAPPER_SYNTHETIC_MODULE_SCRIPT_H_
\ No newline at end of file