BASELINE: Update Chromium to 76.0.3809.94

Change-Id: I321c3f5f929c105aec0f98c5091ef6108822e647
Reviewed-by: Michael Brüning <michael.bruning@qt.io>

20 files changed, 360 insertions, 301 deletions

diff --git a/chromium/components/ntp_tiles/BUILD.gn b/chromium/components/ntp_tiles/BUILD.gn
index 33d2c608dba..244ad33d493 100644
--- a/chromium/components/ntp_tiles/BUILD.gn
+++ b/chromium/components/ntp_tiles/BUILD.gn
@@ -53,7 +53,6 @@ static_library("ntp_tiles") {
     "//components/suggestions",
   ]
   deps = [
-    "//components/data_use_measurement/core",
     "//components/favicon/core",
     "//components/favicon_base",
     "//components/google/core/browser",
@@ -72,22 +71,6 @@ static_library("ntp_tiles") {
   ]
 }
 
-# If you want to use this, let us (ntp-dev@chromium.org) know. In that case, it
-# should be moved to a more common location as it has 2+ callers already.
-# Note that you probably shouldn't be using it outside of ios or tests.
-source_set("json_unsafe_parser") {
-  testonly = !is_ios
-
-  sources = [
-    "json_unsafe_parser.cc",
-    "json_unsafe_parser.h",
-  ]
-
-  public_deps = [
-    "//base",
-  ]
-}
-
 source_set("unit_tests") {
   testonly = true
   sources = [
@@ -100,7 +83,6 @@ source_set("unit_tests") {
   ]
 
   deps = [
-    ":json_unsafe_parser",
     ":ntp_tiles",
     "//base/test:test_support",
     "//components/favicon/core",
@@ -112,6 +94,7 @@ source_set("unit_tests") {
     "//components/rappor:test_support",
     "//components/sync_preferences:test_support",
     "//net:test_support",
+    "//services/data_decoder/public/cpp:test_support",
     "//services/network:test_support",
     "//services/network/public/cpp",
     "//testing/gmock",
diff --git a/chromium/components/ntp_tiles/DEPS b/chromium/components/ntp_tiles/DEPS
index 18f2f118b9b..985869d766a 100644
--- a/chromium/components/ntp_tiles/DEPS
+++ b/chromium/components/ntp_tiles/DEPS
@@ -1,5 +1,4 @@
 include_rules = [
-  "+components/data_use_measurement/core",
   "+components/favicon",
   "+components/favicon_base",
   "+components/google/core",
@@ -18,9 +17,9 @@ include_rules = [
   "+components/variations",
   "+jni",
   "+net",
+  "+services/data_decoder/public/cpp/testing_json_parser.h",
   "+services/network/public/cpp",
   "+services/network/test",
   "+ui/gfx",
   "+ui/base",
 ]
-
diff --git a/chromium/components/ntp_tiles/OWNERS b/chromium/components/ntp_tiles/OWNERS
index e5dfa00fed9..91a328f7120 100644
--- a/chromium/components/ntp_tiles/OWNERS
+++ b/chromium/components/ntp_tiles/OWNERS
@@ -1,4 +1,5 @@
 fhorschig@chromium.org
 jkrcal@chromium.org
+kristipark@chromium.org
 mastiz@chromium.org
 treib@chromium.org
diff --git a/chromium/components/ntp_tiles/constants.cc b/chromium/components/ntp_tiles/constants.cc
index b40488bcd09..ed849b2bf3c 100644
--- a/chromium/components/ntp_tiles/constants.cc
+++ b/chromium/components/ntp_tiles/constants.cc
@@ -4,23 +4,12 @@
 
 #include "components/ntp_tiles/constants.h"
 
-#include "base/feature_list.h"
-#include "ui/base/ui_base_features.h"
-
 namespace ntp_tiles {
 
-const char kPopularSitesFieldTrialName[] = "NTPPopularSites";
-
-const base::Feature kPopularSitesBakedInContentFeature{
-    "NTPPopularSitesBakedInContent", base::FEATURE_ENABLED_BY_DEFAULT};
-
-const base::Feature kNtpMostLikelyFaviconsFromServerFeature{
-    "NTPMostLikelyFaviconsFromServer", base::FEATURE_ENABLED_BY_DEFAULT};
-
-const base::Feature kSiteExplorationUiFeature{
-    "SiteExplorationUi", base::FEATURE_DISABLED_BY_DEFAULT};
+const size_t kMaxNumCustomLinks = 10;
 
-const base::Feature kUsePopularSitesSuggestions{
-    "UsePopularSitesSuggestions", base::FEATURE_ENABLED_BY_DEFAULT};
+// Because the custom links feature has an additional "Add shortcut" button, 9
+// tiles are required to balance the Most Visited rows on the NTP.
+const int kMaxNumMostVisited = 9;
 
 }  // namespace ntp_tiles
diff --git a/chromium/components/ntp_tiles/constants.h b/chromium/components/ntp_tiles/constants.h
index 7395995f975..eb7a95f0b1a 100644
--- a/chromium/components/ntp_tiles/constants.h
+++ b/chromium/components/ntp_tiles/constants.h
@@ -5,29 +5,20 @@
 #ifndef COMPONENTS_NTP_TILES_CONSTANTS_H_
 #define COMPONENTS_NTP_TILES_CONSTANTS_H_
 
-namespace base {
-struct Feature;
-}  // namespace base
+#include <stddef.h>
 
-namespace ntp_tiles {
-
-// Name of the field trial to configure PopularSites.
-extern const char kPopularSitesFieldTrialName[];
+#include <utility>
 
-// This feature is enabled by default. Otherwise, users who need it would not
-// get the right configuration timely enough. The configuration affects only
-// Android or iOS users.
-extern const base::Feature kPopularSitesBakedInContentFeature;
+namespace ntp_tiles {
 
-// Feature to allow the new Google favicon server for fetching favicons for Most
-// Likely tiles on the New Tab Page.
-extern const base::Feature kNtpMostLikelyFaviconsFromServerFeature;
+// Maximum number of custom links that can be set by the user. Used on desktop.
+extern const size_t kMaxNumCustomLinks;
 
-// Feature to provide site exploration tiles in addition to personal tiles.
-extern const base::Feature kSiteExplorationUiFeature;
+// Maximum number of Most Visited sites that will be generated. Used on desktop.
+extern const int kMaxNumMostVisited;
 
-// If this feature is enabled, we enable popular sites in the suggestions UI.
-extern const base::Feature kUsePopularSitesSuggestions;
+// Maximum number of tiles that can be shown on the NTP.
+const int kMaxNumTiles = 10;
 
 }  // namespace ntp_tiles
 
diff --git a/chromium/components/ntp_tiles/custom_links_manager_impl.cc b/chromium/components/ntp_tiles/custom_links_manager_impl.cc
index 75bca9b0393..32b562a39d1 100644
--- a/chromium/components/ntp_tiles/custom_links_manager_impl.cc
+++ b/chromium/components/ntp_tiles/custom_links_manager_impl.cc
@@ -10,18 +10,13 @@
 
 #include "base/auto_reset.h"
 #include "base/bind.h"
+#include "components/ntp_tiles/constants.h"
 #include "components/ntp_tiles/pref_names.h"
 #include "components/pref_registry/pref_registry_syncable.h"
 #include "components/prefs/pref_service.h"
 
 namespace ntp_tiles {
 
-namespace {
-
-const int kMaxNumLinks = 10;
-
-}  // namespace
-
 CustomLinksManagerImpl::CustomLinksManagerImpl(
     PrefService* prefs,
     history::HistoryService* history_service)
@@ -80,7 +75,7 @@ const std::vector<CustomLinksManager::Link>& CustomLinksManagerImpl::GetLinks()
 bool CustomLinksManagerImpl::AddLink(const GURL& url,
                                      const base::string16& title) {
   if (!IsInitialized() || !url.is_valid() ||
-      current_links_.size() == kMaxNumLinks) {
+      current_links_.size() == ntp_tiles::kMaxNumCustomLinks) {
     return false;
   }
 
diff --git a/chromium/components/ntp_tiles/features.cc b/chromium/components/ntp_tiles/features.cc
index d1f3c33814c..0ea51f0746e 100644
--- a/chromium/components/ntp_tiles/features.cc
+++ b/chromium/components/ntp_tiles/features.cc
@@ -9,6 +9,17 @@
 
 namespace ntp_tiles {
 
+const char kPopularSitesFieldTrialName[] = "NTPPopularSites";
+
+const base::Feature kPopularSitesBakedInContentFeature{
+    "NTPPopularSitesBakedInContent", base::FEATURE_ENABLED_BY_DEFAULT};
+
+const base::Feature kNtpMostLikelyFaviconsFromServerFeature{
+    "NTPMostLikelyFaviconsFromServer", base::FEATURE_ENABLED_BY_DEFAULT};
+
+const base::Feature kUsePopularSitesSuggestions{
+    "UsePopularSitesSuggestions", base::FEATURE_ENABLED_BY_DEFAULT};
+
 const base::Feature kDefaultSearchShortcut{"DefaultSearchShortcut",
                                            base::FEATURE_DISABLED_BY_DEFAULT};
 
diff --git a/chromium/components/ntp_tiles/features.h b/chromium/components/ntp_tiles/features.h
index 0c60cfc0d7b..39dc61dcdb2 100644
--- a/chromium/components/ntp_tiles/features.h
+++ b/chromium/components/ntp_tiles/features.h
@@ -11,6 +11,21 @@ struct Feature;
 
 namespace ntp_tiles {
 
+// Name of the field trial to configure PopularSites.
+extern const char kPopularSitesFieldTrialName[];
+
+// This feature is enabled by default. Otherwise, users who need it would not
+// get the right configuration timely enough. The configuration affects only
+// Android or iOS users.
+extern const base::Feature kPopularSitesBakedInContentFeature;
+
+// Feature to allow the new Google favicon server for fetching favicons for Most
+// Likely tiles on the New Tab Page.
+extern const base::Feature kNtpMostLikelyFaviconsFromServerFeature;
+
+// If this feature is enabled, we enable popular sites in the suggestions UI.
+extern const base::Feature kUsePopularSitesSuggestions;
+
 // If enabled, show a Google search shortcut on the NTP by default.
 extern const base::Feature kDefaultSearchShortcut;
 
diff --git a/chromium/components/ntp_tiles/icon_cacher_impl.cc b/chromium/components/ntp_tiles/icon_cacher_impl.cc
index a4a62030462..aadc7ddc205 100644
--- a/chromium/components/ntp_tiles/icon_cacher_impl.cc
+++ b/chromium/components/ntp_tiles/icon_cacher_impl.cc
@@ -18,7 +18,7 @@
 #include "components/favicon_base/favicon_util.h"
 #include "components/image_fetcher/core/image_decoder.h"
 #include "components/image_fetcher/core/image_fetcher.h"
-#include "components/ntp_tiles/constants.h"
+#include "components/ntp_tiles/features.h"
 #include "net/traffic_annotation/network_traffic_annotation.h"
 #include "ui/base/resource/resource_bundle.h"
 #include "ui/gfx/geometry/size.h"
@@ -270,7 +270,8 @@ void IconCacherImpl::OnGetLargeIconOrFallbackStyleFinished(
               page_url,
               GetMinimumFetchingSizeForChromeSuggestionsFaviconsFromServer(),
               GetDesiredFetchingSizeForChromeSuggestionsFaviconsFromServer()),
-          /*may_page_url_be_private=*/true, traffic_annotation,
+          /*may_page_url_be_private=*/true, /*should_trim_page_url_path=*/false,
+          traffic_annotation,
           base::Bind(&IconCacherImpl::OnMostLikelyFaviconDownloaded,
                      weak_ptr_factory_.GetWeakPtr(), page_url));
 }
diff --git a/chromium/components/ntp_tiles/json_unsafe_parser.cc b/chromium/components/ntp_tiles/json_unsafe_parser.cc
deleted file mode 100644
index e1281f00050..00000000000
--- a/chromium/components/ntp_tiles/json_unsafe_parser.cc
+++ /dev/null
@@ -1,41 +0,0 @@
-// Copyright 2016 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 "components/ntp_tiles/json_unsafe_parser.h"
-
-#include "base/bind.h"
-#include "base/callback.h"
-#include "base/json/json_parser.h"
-#include "base/strings/stringprintf.h"
-#include "base/threading/thread_task_runner_handle.h"
-#include "base/values.h"
-
-namespace ntp_tiles {
-
-void JsonUnsafeParser::Parse(const std::string& unsafe_json,
-                             const SuccessCallback& success_callback,
-                             const ErrorCallback& error_callback) {
-  base::ThreadTaskRunnerHandle::Get()->PostTask(
-      FROM_HERE,
-      base::BindOnce(
-          [](const std::string& unsafe_json,
-             const SuccessCallback& success_callback,
-             const ErrorCallback& error_callback) {
-            std::string error_msg;
-            int error_line, error_column;
-            std::unique_ptr<base::Value> value =
-                base::JSONReader::ReadAndReturnErrorDeprecated(
-                    unsafe_json, base::JSON_ALLOW_TRAILING_COMMAS, nullptr,
-                    &error_msg, &error_line, &error_column);
-            if (value) {
-              success_callback.Run(std::move(value));
-            } else {
-              error_callback.Run(base::StringPrintf(
-                  "%s (%d:%d)", error_msg.c_str(), error_line, error_column));
-            }
-          },
-          unsafe_json, success_callback, error_callback));
-}
-
-}  // namespace ntp_tiles
diff --git a/chromium/components/ntp_tiles/json_unsafe_parser.h b/chromium/components/ntp_tiles/json_unsafe_parser.h
deleted file mode 100644
index 4a5a1f47dcd..00000000000
--- a/chromium/components/ntp_tiles/json_unsafe_parser.h
+++ /dev/null
@@ -1,40 +0,0 @@
-// Copyright 2016 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 COMPONENTS_NTP_TILES_JSON_UNSAFE_PARSER_H_
-#define COMPONENTS_NTP_TILES_JSON_UNSAFE_PARSER_H_
-
-#include <memory>
-#include <string>
-
-#include "base/callback_forward.h"
-
-namespace base {
-class Value;
-}
-
-namespace ntp_tiles {
-
-// Mimics SafeJsonParser, but parses unsafely.
-//
-// Do not use this class, unless you can't help it. On most platforms,
-// SafeJsonParser is available and is safer. If it is not available (e.g. on
-// iOS), then this class mimics its API without its safety.
-class JsonUnsafeParser {
- public:
-  using SuccessCallback = base::Callback<void(std::unique_ptr<base::Value>)>;
-  using ErrorCallback = base::Callback<void(const std::string&)>;
-
-  // As with SafeJsonParser, runs either success_callback or error_callback on
-  // the calling thread, but not before the call returns.
-  static void Parse(const std::string& unsafe_json,
-                    const SuccessCallback& success_callback,
-                    const ErrorCallback& error_callback);
-
-  JsonUnsafeParser() = delete;
-};
-
-}  // namespace ntp_tiles
-
-#endif  // COMPONENTS_NTP_TILES_POPULAR_SITES_H_
diff --git a/chromium/components/ntp_tiles/metrics.cc b/chromium/components/ntp_tiles/metrics.cc
index 9cc76163918..8b97fa2fe9d 100644
--- a/chromium/components/ntp_tiles/metrics.cc
+++ b/chromium/components/ntp_tiles/metrics.cc
@@ -9,6 +9,7 @@
 #include "base/metrics/histogram_functions.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/strings/stringprintf.h"
+#include "components/ntp_tiles/constants.h"
 #include "components/rappor/public/rappor_utils.h"
 
 namespace ntp_tiles {
@@ -16,9 +17,6 @@ namespace metrics {
 
 namespace {
 
-// Maximum number of tiles to record in histograms.
-const int kMaxNumTiles = 12;
-
 const int kLastTitleSource = static_cast<int>(TileTitleSource::LAST);
 
 // Identifiers for the various tile sources.
@@ -29,6 +27,7 @@ const char kHistogramBakedInName[] = "popular_baked_in";
 const char kHistogramWhitelistName[] = "whitelist";
 const char kHistogramHomepageName[] = "homepage";
 const char kHistogramCustomLinksName[] = "custom_links";
+const char kHistogramExploreName[] = "explore";
 const char kHistogramSearchName[] = "search_page";
 
 // Suffixes for the various icon types.
@@ -60,6 +59,8 @@ std::string GetSourceHistogramName(TileSource source) {
       return kHistogramHomepageName;
     case TileSource::CUSTOM_LINKS:
       return kHistogramCustomLinksName;
+    case TileSource::EXPLORE:
+      return kHistogramExploreName;
     case TileSource::SEARCH_PAGE:
       return kHistogramSearchName;
   }
diff --git a/chromium/components/ntp_tiles/most_visited_sites.cc b/chromium/components/ntp_tiles/most_visited_sites.cc
index e643df1701a..e4744670b75 100644
--- a/chromium/components/ntp_tiles/most_visited_sites.cc
+++ b/chromium/components/ntp_tiles/most_visited_sites.cc
@@ -6,6 +6,7 @@
 
 #include <algorithm>
 #include <iterator>
+#include <memory>
 #include <utility>
 
 #include "base/bind.h"
@@ -37,10 +38,6 @@ namespace ntp_tiles {
 
 namespace {
 
-// The maximum number of custom links that can be shown. This is independent of
-// the maximum number of Most Visited sites that can be shown.
-const size_t kMaxNumCustomLinks = 10;
-
 const base::Feature kDisplaySuggestionsServiceTiles{
     "DisplaySuggestionsServiceTiles", base::FEATURE_ENABLED_BY_DEFAULT};
 
@@ -60,11 +57,9 @@ const char* kKnownGenericPagePrefixes[] = {
     ""};  // The no-www domain matches domains on same level .
 
 // Determine whether we need any tiles from PopularSites to fill up a grid of
-// |num_tiles| tiles. If exploration sections are used, we need popular sites
-// regardless of how many tiles we already have.
+// |num_tiles| tiles.
 bool NeedPopularSites(const PrefService* prefs, int num_tiles) {
-  return base::FeatureList::IsEnabled(kSiteExplorationUiFeature) ||
-         prefs->GetInteger(prefs::kNumPersonalTiles) < num_tiles;
+  return prefs->GetInteger(prefs::kNumPersonalTiles) < num_tiles;
 }
 
 bool AreURLsEquivalent(const GURL& url1, const GURL& url2) {
@@ -189,6 +184,8 @@ bool MostVisitedSites::DoesSourceExist(TileSource source) const {
       return supervisor_ != nullptr;
     case TileSource::CUSTOM_LINKS:
       return custom_links_ != nullptr;
+    case TileSource::EXPLORE:
+      return explore_sites_client_ != nullptr;
     case TileSource::SEARCH_PAGE:
 #if !defined(OS_ANDROID) && !defined(OS_IOS)
       return true;
@@ -206,6 +203,11 @@ void MostVisitedSites::SetHomepageClient(
   homepage_client_ = std::move(client);
 }
 
+void MostVisitedSites::SetExploreSitesClient(
+    std::unique_ptr<ExploreSitesClient> client) {
+  explore_sites_client_ = std::move(client);
+}
+
 void MostVisitedSites::SetMostVisitedURLsObserver(Observer* observer,
                                                   size_t num_sites) {
   DCHECK(observer);
@@ -295,6 +297,7 @@ bool MostVisitedSites::AddCustomLink(const GURL& url,
   if (!custom_links_ || !custom_links_enabled_)
     return false;
 
+  bool is_first_action = !custom_links_->IsInitialized();
   // Initialize custom links if they have not been initialized yet.
   InitializeCustomLinks();
 
@@ -303,6 +306,10 @@ bool MostVisitedSites::AddCustomLink(const GURL& url,
     if (custom_links_action_count_ != -1)
       custom_links_action_count_++;
     BuildCurrentTiles();
+  } else if (is_first_action) {
+    // We don't want to keep custom links initialized if the first action after
+    // initialization failed.
+    UninitializeCustomLinks();
   }
   return success;
 }
@@ -313,6 +320,7 @@ bool MostVisitedSites::UpdateCustomLink(const GURL& url,
   if (!custom_links_ || !custom_links_enabled_)
     return false;
 
+  bool is_first_action = !custom_links_->IsInitialized();
   // Initialize custom links if they have not been initialized yet.
   InitializeCustomLinks();
 
@@ -321,6 +329,10 @@ bool MostVisitedSites::UpdateCustomLink(const GURL& url,
     if (custom_links_action_count_ != -1)
       custom_links_action_count_++;
     BuildCurrentTiles();
+  } else if (is_first_action) {
+    // We don't want to keep custom links initialized if the first action after
+    // initialization failed.
+    UninitializeCustomLinks();
   }
   return success;
 }
@@ -329,6 +341,7 @@ bool MostVisitedSites::ReorderCustomLink(const GURL& url, size_t new_pos) {
   if (!custom_links_ || !custom_links_enabled_)
     return false;
 
+  bool is_first_action = !custom_links_->IsInitialized();
   // Initialize custom links if they have not been initialized yet.
   InitializeCustomLinks();
 
@@ -337,6 +350,10 @@ bool MostVisitedSites::ReorderCustomLink(const GURL& url, size_t new_pos) {
     if (custom_links_action_count_ != -1)
       custom_links_action_count_++;
     BuildCurrentTiles();
+  } else if (is_first_action) {
+    // We don't want to keep custom links initialized if the first action after
+    // initialization failed.
+    UninitializeCustomLinks();
   }
   return success;
 }
@@ -345,6 +362,7 @@ bool MostVisitedSites::DeleteCustomLink(const GURL& url) {
   if (!custom_links_ || !custom_links_enabled_)
     return false;
 
+  bool is_first_action = !custom_links_->IsInitialized();
   // Initialize custom links if they have not been initialized yet.
   InitializeCustomLinks();
 
@@ -353,6 +371,10 @@ bool MostVisitedSites::DeleteCustomLink(const GURL& url) {
     if (custom_links_action_count_ != -1)
       custom_links_action_count_++;
     BuildCurrentTiles();
+  } else if (is_first_action) {
+    // We don't want to keep custom links initialized if the first action after
+    // initialization failed.
+    UninitializeCustomLinks();
   }
   return success;
 }
@@ -707,6 +729,19 @@ NTPTilesVector MostVisitedSites::InsertHomeTile(
   return new_tiles;
 }
 
+base::Optional<NTPTile> MostVisitedSites::CreateExploreSitesTile() {
+  if (!explore_sites_client_)
+    return base::nullopt;
+
+  NTPTile explore_sites_tile;
+  explore_sites_tile.url = explore_sites_client_->GetExploreSitesUrl();
+  explore_sites_tile.title = explore_sites_client_->GetExploreSitesTitle();
+  explore_sites_tile.source = TileSource::EXPLORE;
+  explore_sites_tile.title_source = TileTitleSource::UNKNOWN;
+
+  return explore_sites_tile;
+}
+
 NTPTilesVector MostVisitedSites::InsertSearchTile(NTPTilesVector tiles) const {
   DCHECK_GT(max_num_sites_, 0u);
 
@@ -771,6 +806,8 @@ void MostVisitedSites::BuildCustomLinks(
   DCHECK(custom_links_);
 
   NTPTilesVector tiles;
+  // The maximum number of custom links that can be shown is independent of the
+  // maximum number of Most Visited sites that can be shown.
   size_t num_tiles = std::min(links.size(), kMaxNumCustomLinks);
   for (size_t i = 0; i < num_tiles; ++i) {
     const CustomLinksManager::Link& link = links.at(i);
@@ -813,7 +850,15 @@ void MostVisitedSites::InitiateNotificationForNewTiles(
 
 void MostVisitedSites::MergeMostVisitedTiles(NTPTilesVector personal_tiles) {
   std::set<std::string> used_hosts;
-  size_t num_actual_tiles = 0u;
+
+  base::Optional<NTPTile> explore_tile = CreateExploreSitesTile();
+  size_t num_actual_tiles = explore_tile ? 1 : 0;
+
+  // The explore sites tile may have taken a space that was utilized by the
+  // personal tiles.
+  if (personal_tiles.size() + num_actual_tiles > max_num_sites_) {
+    personal_tiles.pop_back();
+  }
   AddToHostsAndTotalCount(personal_tiles, &used_hosts, &num_actual_tiles);
 
   NTPTilesVector whitelist_tiles =
@@ -827,7 +872,7 @@ void MostVisitedSites::MergeMostVisitedTiles(NTPTilesVector personal_tiles) {
 
   NTPTilesVector new_tiles =
       MergeTiles(std::move(personal_tiles), std::move(whitelist_tiles),
-                 std::move(sections[SectionType::PERSONALIZED]));
+                 std::move(sections[SectionType::PERSONALIZED]), explore_tile);
 
   SaveTilesAndNotify(std::move(new_tiles), std::move(sections));
 }
@@ -854,9 +899,11 @@ void MostVisitedSites::SaveTilesAndNotify(
 }
 
 // static
-NTPTilesVector MostVisitedSites::MergeTiles(NTPTilesVector personal_tiles,
-                                            NTPTilesVector whitelist_tiles,
-                                            NTPTilesVector popular_tiles) {
+NTPTilesVector MostVisitedSites::MergeTiles(
+    NTPTilesVector personal_tiles,
+    NTPTilesVector whitelist_tiles,
+    NTPTilesVector popular_tiles,
+    base::Optional<NTPTile> explore_tile) {
   NTPTilesVector merged_tiles;
   std::move(personal_tiles.begin(), personal_tiles.end(),
             std::back_inserter(merged_tiles));
@@ -864,6 +911,9 @@ NTPTilesVector MostVisitedSites::MergeTiles(NTPTilesVector personal_tiles,
             std::back_inserter(merged_tiles));
   std::move(popular_tiles.begin(), popular_tiles.end(),
             std::back_inserter(merged_tiles));
+  if (explore_tile)
+    merged_tiles.push_back(*explore_tile);
+
   return merged_tiles;
 }
 
diff --git a/chromium/components/ntp_tiles/most_visited_sites.h b/chromium/components/ntp_tiles/most_visited_sites.h
index edcb280a039..e2e349e2a0f 100644
--- a/chromium/components/ntp_tiles/most_visited_sites.h
+++ b/chromium/components/ntp_tiles/most_visited_sites.h
@@ -113,6 +113,13 @@ class MostVisitedSites : public history::TopSitesObserver,
     virtual void QueryHomepageTitle(TitleCallback title_callback) = 0;
   };
 
+  class ExploreSitesClient {
+   public:
+    virtual ~ExploreSitesClient() = default;
+    virtual GURL GetExploreSitesUrl() const = 0;
+    virtual base::string16 GetExploreSitesTitle() const = 0;
+  };
+
   // Construct a MostVisitedSites instance.
   //
   // |prefs| and |suggestions| are required and may not be null. |top_sites|,
@@ -152,6 +159,10 @@ class MostVisitedSites : public history::TopSitesObserver,
   // |client| must not be null and outlive this object.
   void SetHomepageClient(std::unique_ptr<HomepageClient> client);
 
+  // Sets the client that provides the Explore Sites tile. Can be null if no
+  // such tile is desirable.
+  void SetExploreSitesClient(std::unique_ptr<ExploreSitesClient> client);
+
   // Requests an asynchronous refresh of the suggestions. Notifies the observer
   // if the request resulted in the set of tiles changing.
   void Refresh();
@@ -176,24 +187,25 @@ class MostVisitedSites : public history::TopSitesObserver,
   void EnableCustomLinks(bool enable);
   // Adds a custom link. If the number of current links is maxed, returns false
   // and does nothing. Will initialize custom links if they have not been
-  // initialized yet. Custom links must be enabled.
+  // initialized yet, unless the action fails. Custom links must be enabled.
   bool AddCustomLink(const GURL& url, const base::string16& title);
   // Updates the URL and/or title of the custom link specified by |url|. If
   // |url| does not exist or |new_url| already exists in the custom link list,
   // returns false and does nothing. Will initialize custom links if they have
-  // not been initialized yet. Custom links must be enabled.
+  // not been initialized yet, unless the action fails. Custom links must be
+  // enabled.
   bool UpdateCustomLink(const GURL& url,
                         const GURL& new_url,
                         const base::string16& new_title);
   // Moves the custom link specified by |url| to the index |new_pos|. If |url|
   // does not exist, or |new_pos| is invalid, returns false and does nothing.
-  // Will initialize custom links if they have not been initialized yet. Custom
-  // links must be enabled.
+  // Will initialize custom links if they have not been initialized yet, unless
+  // the action fails. Custom links must be enabled.
   bool ReorderCustomLink(const GURL& url, size_t new_pos);
   // Deletes the custom link with the specified |url|. If |url| does not exist
   // in the custom link list, returns false and does nothing. Will initialize
-  // custom links if they have not been initialized yet. Custom links must be
-  // enabled.
+  // custom links if they have not been initialized yet, unless the action
+  // fails. Custom links must be enabled.
   bool DeleteCustomLink(const GURL& url);
   // Restores the previous state of custom links before the last action that
   // modified them. If there was no action, does nothing. If this is undoing the
@@ -213,7 +225,8 @@ class MostVisitedSites : public history::TopSitesObserver,
   // public method for ease of testing.
   static NTPTilesVector MergeTiles(NTPTilesVector personal_tiles,
                                    NTPTilesVector whitelist_tiles,
-                                   NTPTilesVector popular_tiles);
+                                   NTPTilesVector popular_tiles,
+                                   base::Optional<NTPTile> explore_tile);
 
  private:
   FRIEND_TEST_ALL_PREFIXES(MostVisitedSitesTest,
@@ -309,6 +322,10 @@ class MostVisitedSites : public history::TopSitesObserver,
   NTPTilesVector InsertHomeTile(NTPTilesVector tiles,
                                 const base::string16& title) const;
 
+  // Creates a tile for the Explore Sites page, if enabled. The tile is added to
+  // the front of the list.
+  base::Optional<NTPTile> CreateExploreSitesTile();
+
   // Adds the Google Search page as first tile to |tiles| and returns them as
   // new vector. Drops existing tiles with the same host as the Google Search
   // page and tiles that would exceed the maximum.
@@ -333,6 +350,7 @@ class MostVisitedSites : public history::TopSitesObserver,
   std::unique_ptr<IconCacher> const icon_cacher_;
   std::unique_ptr<MostVisitedSitesSupervisor> supervisor_;
   std::unique_ptr<HomepageClient> homepage_client_;
+  std::unique_ptr<ExploreSitesClient> explore_sites_client_;
 
   Observer* observer_;
 
diff --git a/chromium/components/ntp_tiles/most_visited_sites_unittest.cc b/chromium/components/ntp_tiles/most_visited_sites_unittest.cc
index fe08f7a1442..129a07c789f 100644
--- a/chromium/components/ntp_tiles/most_visited_sites_unittest.cc
+++ b/chromium/components/ntp_tiles/most_visited_sites_unittest.cc
@@ -27,16 +27,15 @@
 #include "build/build_config.h"
 #include "components/history/core/browser/top_sites.h"
 #include "components/history/core/browser/top_sites_observer.h"
-#include "components/ntp_tiles/constants.h"
 #include "components/ntp_tiles/custom_links_manager.h"
 #include "components/ntp_tiles/features.h"
 #include "components/ntp_tiles/icon_cacher.h"
-#include "components/ntp_tiles/json_unsafe_parser.h"
 #include "components/ntp_tiles/popular_sites_impl.h"
 #include "components/ntp_tiles/pref_names.h"
 #include "components/ntp_tiles/section_type.h"
 #include "components/ntp_tiles/switches.h"
 #include "components/sync_preferences/testing_pref_service_syncable.h"
+#include "services/data_decoder/public/cpp/testing_json_parser.h"
 #include "services/network/public/cpp/shared_url_loader_factory.h"
 #include "services/network/public/cpp/weak_wrapper_shared_url_loader_factory.h"
 #include "services/network/test/test_url_loader_factory.h"
@@ -83,6 +82,8 @@ using testing::_;
 
 const char kHomepageUrl[] = "http://ho.me/";
 const char kHomepageTitle[] = "Home";
+const char kTestExploreUrl[] = "https://example.com/";
+const char kTestExploreTitle[] = "Example";
 
 std::string PrintTile(const std::string& title,
                       const std::string& url,
@@ -102,6 +103,29 @@ MATCHER_P3(MatchesTile, title, url, source, PrintTile(title, url, source)) {
          arg.source == source;
 }
 
+std::string PrintTileSource(TileSource source) {
+  return std::string("has source ") +
+         testing::PrintToString(static_cast<int>(source));
+}
+
+MATCHER_P(TileWithSource, source, PrintTileSource(source)) {
+  return arg.source == source;
+}
+
+MATCHER_P3(LastTileIs,
+           title,
+           url,
+           source,
+           std::string("last tile ") + PrintTile(title, url, source)) {
+  const NTPTilesVector& tiles = arg.at(SectionType::PERSONALIZED);
+  if (tiles.empty())
+    return false;
+
+  const NTPTile& last = tiles.back();
+  return last.title == base::ASCIIToUTF16(title) && last.url == GURL(url) &&
+         last.source == source;
+}
+
 MATCHER_P3(FirstPersonalizedTileIs,
            title,
            url,
@@ -243,6 +267,17 @@ class FakeHomepageClient : public MostVisitedSites::HomepageClient {
   base::Optional<base::string16> homepage_title_;
 };
 
+class FakeExploreSitesClient : public MostVisitedSites::ExploreSitesClient {
+ public:
+  ~FakeExploreSitesClient() override = default;
+
+  GURL GetExploreSitesUrl() const override { return GURL(kTestExploreUrl); }
+
+  base::string16 GetExploreSitesTitle() const override {
+    return base::ASCIIToUTF16(kTestExploreTitle);
+  }
+};
+
 class MockIconCacher : public IconCacher {
  public:
   MOCK_METHOD3(StartFetchPopularSites,
@@ -299,7 +334,7 @@ class PopularSitesFactoryForTest {
               "title": "PopularSite2",
               "url": "http://popularsite2/",
               "favicon_url": "http://popularsite2/favicon.ico"
-            },
+            }
            ])");
 
     test_url_loader_factory_.AddResponse(
@@ -316,7 +351,7 @@ class PopularSitesFactoryForTest {
               "title": "Google News",
               "url": "http://news.google.com",
               "favicon_url": "http://news.google.com/favicon.ico"
-            },
+            }
            ])");
 
     test_url_loader_factory_.AddResponse(
@@ -370,7 +405,7 @@ class PopularSitesFactoryForTest {
         prefs_,
         /*template_url_service=*/nullptr,
         /*variations_service=*/nullptr, test_shared_loader_factory_,
-        base::Bind(JsonUnsafeParser::Parse));
+        base::Bind(&data_decoder::SafeJsonParser::Parse, nullptr));
   }
 
  private:
@@ -502,6 +537,13 @@ class MostVisitedSitesTest : public ::testing::TestWithParam<bool> {
     return raw_client_ptr;
   }
 
+  FakeExploreSitesClient* RegisterNewExploreSitesClient() {
+    auto explore_sites_client = std::make_unique<FakeExploreSitesClient>();
+    FakeExploreSitesClient* raw_client_ptr = explore_sites_client.get();
+    most_visited_sites_->SetExploreSitesClient(std::move(explore_sites_client));
+    return raw_client_ptr;
+  }
+
   void DisableRemoteSuggestions() {
     EXPECT_CALL(mock_suggestions_service_, AddCallback(_))
         .Times(AnyNumber())
@@ -523,6 +565,7 @@ class MostVisitedSitesTest : public ::testing::TestWithParam<bool> {
   TopSitesCallbackList top_sites_callbacks_;
 
   base::test::ScopedTaskEnvironment task_environment_;
+  data_decoder::TestingJsonParser::ScopedFactoryOverride factory_override_;
   sync_preferences::TestingPrefServiceSyncable pref_service_;
   PopularSitesFactoryForTest popular_sites_factory_;
   scoped_refptr<StrictMock<MockTopSites>> mock_top_sites_;
@@ -867,6 +910,71 @@ TEST_P(MostVisitedSitesTest, ShouldPinHomepageAgainIfBlacklistingUndone) {
   base::RunLoop().RunUntilIdle();
 }
 
+TEST_P(MostVisitedSitesTest, ShouldNotIncludeTileForExploreSitesIfNoClient) {
+  // Does not register an explore sites client.
+
+  DisableRemoteSuggestions();
+  EXPECT_CALL(*mock_top_sites_, GetMostVisitedURLs(_))
+      .WillRepeatedly(InvokeCallbackArgument<0>(MostVisitedURLList{
+          MakeMostVisitedURL("ESPN", "http://espn.com/"),
+          MakeMostVisitedURL("Mobile", "http://m.mobile.de/"),
+          MakeMostVisitedURL("Google", "http://www.google.com/")}));
+  EXPECT_CALL(*mock_top_sites_, SyncWithHistory());
+  EXPECT_CALL(mock_observer_,
+              OnURLsAvailable(Not(Contains(
+                  Pair(SectionType::PERSONALIZED,
+                       Contains(TileWithSource(TileSource::EXPLORE)))))));
+  // Note that 5 sites are requested, this means that there should be the 3 from
+  // top sites and two from popular sites.
+  most_visited_sites_->SetMostVisitedURLsObserver(&mock_observer_,
+                                                  /*num_sites=*/5);
+  base::RunLoop().RunUntilIdle();
+}
+
+// Tests that the explore sites tile appears when there is a mix of top sites
+// and popular sites.
+TEST_P(MostVisitedSitesTest, ShouldIncludeTileForExploreSites) {
+  RegisterNewExploreSitesClient();
+  DisableRemoteSuggestions();
+  EXPECT_CALL(*mock_top_sites_, GetMostVisitedURLs(_))
+      .WillRepeatedly(InvokeCallbackArgument<0>(MostVisitedURLList{
+          MakeMostVisitedURL("ESPN", "http://espn.com/"),
+          MakeMostVisitedURL("Mobile", "http://m.mobile.de/"),
+          MakeMostVisitedURL("Google", "http://www.google.com/")}));
+  EXPECT_CALL(*mock_top_sites_, SyncWithHistory());
+  EXPECT_CALL(mock_observer_,
+              OnURLsAvailable(LastTileIs(kTestExploreTitle, kTestExploreUrl,
+                                         TileSource::EXPLORE)));
+  // Note that 5 sites are requested, this means that there should be the 3 from
+  // top sites, one from popular sites, and one explore tile.
+  most_visited_sites_->SetMostVisitedURLsObserver(&mock_observer_,
+                                                  /*num_sites=*/5);
+  base::RunLoop().RunUntilIdle();
+}
+
+TEST_P(MostVisitedSitesTest, RemovesPersonalSiteIfExploreSitesTilePresent) {
+  RegisterNewExploreSitesClient();
+  DisableRemoteSuggestions();
+  EXPECT_CALL(*mock_top_sites_, GetMostVisitedURLs(_))
+      .WillRepeatedly(InvokeCallbackArgument<0>(MostVisitedURLList{
+          MakeMostVisitedURL("ESPN", "http://espn.com/"),
+          MakeMostVisitedURL("Mobile", "http://m.mobile.de/"),
+          MakeMostVisitedURL("Google", "http://www.google.com/")}));
+  EXPECT_CALL(*mock_top_sites_, SyncWithHistory());
+  EXPECT_CALL(mock_observer_,
+              OnURLsAvailable(Contains(Pair(
+                  SectionType::PERSONALIZED,
+                  ElementsAre(MatchesTile("ESPN", "http://espn.com/",
+                                          TileSource::TOP_SITES),
+                              MatchesTile("Mobile", "http://m.mobile.de/",
+                                          TileSource::TOP_SITES),
+                              MatchesTile(kTestExploreTitle, kTestExploreUrl,
+                                          TileSource::EXPLORE))))));
+  most_visited_sites_->SetMostVisitedURLsObserver(&mock_observer_,
+                                                  /*num_sites=*/3);
+  base::RunLoop().RunUntilIdle();
+}
+
 TEST_P(MostVisitedSitesTest, ShouldInformSuggestionSourcesWhenBlacklisting) {
   EXPECT_CALL(*mock_top_sites_, AddBlacklistedURL(Eq(GURL(kHomepageUrl))))
       .Times(1);
@@ -883,51 +991,6 @@ TEST_P(MostVisitedSitesTest, ShouldInformSuggestionSourcesWhenBlacklisting) {
                                                  /*add_url=*/false);
 }
 
-TEST_P(MostVisitedSitesTest, ShouldContainSiteExplorationsWhenFeatureEnabled) {
-  base::test::ScopedFeatureList feature_list;
-  std::map<SectionType, NTPTilesVector> sections;
-  feature_list.InitAndEnableFeature(kSiteExplorationUiFeature);
-  pref_service_.SetString(prefs::kPopularSitesOverrideVersion, "6");
-  RecreateMostVisitedSites();  // Refills cache with version 6 popular sites.
-  DisableRemoteSuggestions();
-  EXPECT_CALL(*mock_top_sites_, GetMostVisitedURLs(_))
-      .WillRepeatedly(InvokeCallbackArgument<0>(
-          MostVisitedURLList{MakeMostVisitedURL("Site 1", "http://site1/")}));
-  EXPECT_CALL(*mock_top_sites_, SyncWithHistory());
-  EXPECT_CALL(mock_observer_, OnURLsAvailable(_))
-      .WillOnce(SaveArg<0>(&sections));
-
-  most_visited_sites_->SetMostVisitedURLsObserver(&mock_observer_,
-                                                  /*num_sites=*/3);
-  base::RunLoop().RunUntilIdle();
-
-  if (!IsPopularSitesFeatureEnabled()) {
-    EXPECT_THAT(
-        sections,
-        Contains(Pair(SectionType::PERSONALIZED,
-                      ElementsAre(MatchesTile("Site 1", "http://site1/",
-                                              TileSource::TOP_SITES)))));
-    return;
-  }
-  const auto& expected_sections =
-      most_visited_sites_->popular_sites()->sections();
-  ASSERT_THAT(expected_sections.size(), Ge(2ul));
-  EXPECT_THAT(sections.size(), Eq(expected_sections.size()));
-  EXPECT_THAT(
-      sections,
-      AllOf(Contains(Pair(
-                SectionType::PERSONALIZED,
-                ElementsAre(MatchesTile("Site 1", "http://site1/",
-                                        TileSource::TOP_SITES),
-                            MatchesTile("PopularSite1", "http://popularsite1/",
-                                        TileSource::POPULAR),
-                            MatchesTile("PopularSite2", "http://popularsite2/",
-                                        TileSource::POPULAR)))),
-            Contains(Pair(SectionType::NEWS, SizeIs(2ul))),
-            Contains(Pair(SectionType::SOCIAL, SizeIs(1ul))),
-            Contains(Pair(_, IsEmpty()))));
-}
-
 TEST_P(MostVisitedSitesTest,
        ShouldDeduplicatePopularSitesWithMostVisitedIffHostAndTitleMatches) {
   pref_service_.SetString(prefs::kPopularSitesOverrideCountry, "US");
@@ -1515,7 +1578,8 @@ TEST_P(MostVisitedSitesWithCustomLinksTest,
   // Complete a second custom link action.
   EXPECT_CALL(*mock_custom_links_, Initialize(_)).WillOnce(Return(false));
   EXPECT_CALL(*mock_custom_links_, DeleteLink(_)).WillOnce(Return(true));
-  EXPECT_CALL(*mock_custom_links_, IsInitialized()).WillOnce(Return(true));
+  EXPECT_CALL(*mock_custom_links_, IsInitialized())
+      .WillRepeatedly(Return(true));
   EXPECT_CALL(*mock_custom_links_, GetLinks())
       .WillOnce(ReturnRef(expected_links));
   most_visited_sites_->DeleteCustomLink(GURL("test.com"));
@@ -1531,6 +1595,73 @@ TEST_P(MostVisitedSitesWithCustomLinksTest,
   base::RunLoop().RunUntilIdle();
 }
 
+TEST_P(MostVisitedSitesWithCustomLinksTest,
+       UninitializeCustomLinksIfFirstActionFails) {
+  const char kTestUrl[] = "http://site1/";
+  const char kTestTitle[] = "Site 1";
+  std::vector<CustomLinksManager::Link> expected_links(
+      {CustomLinksManager::Link{GURL(kTestUrl),
+                                base::UTF8ToUTF16(kTestTitle)}});
+  std::map<SectionType, NTPTilesVector> sections;
+  DisableRemoteSuggestions();
+
+  // Build initial tiles with Top Sites.
+  EXPECT_CALL(*mock_custom_links_, RegisterCallbackForOnChanged(_));
+  ExpectBuildWithTopSites(
+      MostVisitedURLList{MakeMostVisitedURL(kTestTitle, kTestUrl)}, &sections);
+  most_visited_sites_->SetMostVisitedURLsObserver(&mock_observer_,
+                                                  /*num_sites=*/1);
+  base::RunLoop().RunUntilIdle();
+  ASSERT_THAT(
+      sections.at(SectionType::PERSONALIZED),
+      ElementsAre(MatchesTile(kTestTitle, kTestUrl, TileSource::TOP_SITES)));
+
+  // Fail to add a custom link. This should not initialize custom links nor
+  // notify.
+  EXPECT_CALL(*mock_custom_links_, Initialize(_)).WillOnce(Return(true));
+  EXPECT_CALL(*mock_custom_links_, AddLink(_, _)).WillOnce(Return(false));
+  EXPECT_CALL(*mock_custom_links_, IsInitialized())
+      .WillRepeatedly(Return(false));
+  EXPECT_CALL(*mock_custom_links_, Uninitialize());
+  EXPECT_CALL(mock_observer_, OnURLsAvailable(_)).Times(0);
+  most_visited_sites_->AddCustomLink(GURL(kTestUrl), base::UTF8ToUTF16("test"));
+  base::RunLoop().RunUntilIdle();
+
+  // Fail to edit a custom link. This should not initialize custom links nor
+  // notify.
+  EXPECT_CALL(*mock_custom_links_, Initialize(_)).WillOnce(Return(true));
+  EXPECT_CALL(*mock_custom_links_, UpdateLink(_, _, _)).WillOnce(Return(false));
+  EXPECT_CALL(*mock_custom_links_, IsInitialized())
+      .WillRepeatedly(Return(false));
+  EXPECT_CALL(*mock_custom_links_, Uninitialize());
+  EXPECT_CALL(mock_observer_, OnURLsAvailable(_)).Times(0);
+  most_visited_sites_->UpdateCustomLink(GURL("test.com"), GURL("test2.com"),
+                                        base::UTF8ToUTF16("test"));
+  base::RunLoop().RunUntilIdle();
+
+  // Fail to reorder a custom link. This should not initialize custom links nor
+  // notify.
+  EXPECT_CALL(*mock_custom_links_, Initialize(_)).WillOnce(Return(true));
+  EXPECT_CALL(*mock_custom_links_, ReorderLink(_, _)).WillOnce(Return(false));
+  EXPECT_CALL(*mock_custom_links_, IsInitialized())
+      .WillRepeatedly(Return(false));
+  EXPECT_CALL(*mock_custom_links_, Uninitialize());
+  EXPECT_CALL(mock_observer_, OnURLsAvailable(_)).Times(0);
+  most_visited_sites_->ReorderCustomLink(GURL("test.com"), 1);
+  base::RunLoop().RunUntilIdle();
+
+  // Fail to delete a custom link. This should not initialize custom links nor
+  // notify.
+  EXPECT_CALL(*mock_custom_links_, Initialize(_)).WillOnce(Return(true));
+  EXPECT_CALL(*mock_custom_links_, DeleteLink(_)).WillOnce(Return(false));
+  EXPECT_CALL(*mock_custom_links_, IsInitialized())
+      .WillRepeatedly(Return(false));
+  EXPECT_CALL(*mock_custom_links_, Uninitialize());
+  EXPECT_CALL(mock_observer_, OnURLsAvailable(_)).Times(0);
+  most_visited_sites_->DeleteCustomLink(GURL("test.com"));
+  base::RunLoop().RunUntilIdle();
+}
+
 TEST_P(MostVisitedSitesWithCustomLinksTest, RebuildTilesOnCustomLinksChanged) {
   const char kTestUrl1[] = "http://site1/";
   const char kTestUrl2[] = "http://site2/";
@@ -2062,7 +2193,8 @@ TEST(MostVisitedSitesMergeTest, ShouldMergeTilesWithPersonalOnly) {
   // tiles.
   EXPECT_THAT(MostVisitedSites::MergeTiles(std::move(personal_tiles),
                                            /*whitelist_tiles=*/NTPTilesVector(),
-                                           /*popular_tiles=*/NTPTilesVector()),
+                                           /*popular_tiles=*/NTPTilesVector(),
+                                           /*explore_tile=*/base::nullopt),
               ElementsAre(MatchesTile("Site 1", "https://www.site1.com/",
                                       TileSource::TOP_SITES),
                           MatchesTile("Site 2", "https://www.site2.com/",
@@ -2085,7 +2217,8 @@ TEST(MostVisitedSitesMergeTest, ShouldMergeTilesWithPopularOnly) {
   EXPECT_THAT(
       MostVisitedSites::MergeTiles(/*personal_tiles=*/NTPTilesVector(),
                                    /*whitelist_tiles=*/NTPTilesVector(),
-                                   /*popular_tiles=*/std::move(popular_tiles)),
+                                   /*popular_tiles=*/std::move(popular_tiles),
+                                   /*explore_tile=*/base::nullopt),
       ElementsAre(
           MatchesTile("Site 1", "https://www.site1.com/", TileSource::POPULAR),
           MatchesTile("Site 2", "https://www.site2.com/", TileSource::POPULAR),
@@ -2103,18 +2236,23 @@ TEST(MostVisitedSitesMergeTest, ShouldMergeTilesFavoringPersonalOverPopular) {
       MakeTile("Site 3", "https://www.site3.com/", TileSource::TOP_SITES),
       MakeTile("Site 4", "https://www.site4.com/", TileSource::TOP_SITES),
   };
+  base::Optional<NTPTile> explore_tile{
+      MakeTile("Explore", "https://explore.example.com/", TileSource::EXPLORE),
+  };
   EXPECT_THAT(
       MostVisitedSites::MergeTiles(std::move(personal_tiles),
                                    /*whitelist_tiles=*/NTPTilesVector(),
-                                   /*popular_tiles=*/std::move(popular_tiles)),
+                                   /*popular_tiles=*/std::move(popular_tiles),
+                                   /*explore_tiles=*/explore_tile),
       ElementsAre(
           MatchesTile("Site 3", "https://www.site3.com/",
                       TileSource::TOP_SITES),
           MatchesTile("Site 4", "https://www.site4.com/",
                       TileSource::TOP_SITES),
           MatchesTile("Site 1", "https://www.site1.com/", TileSource::POPULAR),
-          MatchesTile("Site 2", "https://www.site2.com/",
-                      TileSource::POPULAR)));
+          MatchesTile("Site 2", "https://www.site2.com/", TileSource::POPULAR),
+          MatchesTile("Explore", "https://explore.example.com/",
+                      TileSource::EXPLORE)));
 }
 
 #if !defined(OS_ANDROID) && !defined(OS_IOS)
diff --git a/chromium/components/ntp_tiles/popular_sites_impl.cc b/chromium/components/ntp_tiles/popular_sites_impl.cc
index 02380d5d43a..34eef87fd84 100644
--- a/chromium/components/ntp_tiles/popular_sites_impl.cc
+++ b/chromium/components/ntp_tiles/popular_sites_impl.cc
@@ -19,9 +19,8 @@
 #include "base/time/time.h"
 #include "base/values.h"
 #include "build/build_config.h"
-#include "components/data_use_measurement/core/data_use_user_data.h"
 #include "components/google/core/common/google_util.h"
-#include "components/ntp_tiles/constants.h"
+#include "components/ntp_tiles/features.h"
 #include "components/ntp_tiles/pref_names.h"
 #include "components/ntp_tiles/switches.h"
 #include "components/pref_registry/pref_registry_syncable.h"
@@ -172,9 +171,10 @@ std::map<SectionType, PopularSites::SitesVector> ParseVersion6OrAbove(
                    << "invalid ID (" << section << ")";
       continue;
     }
+    // Non-personalized site exploration tiles are no longer supported, so
+    // ignore all other section types.
     SectionType section_type = static_cast<SectionType>(section);
-    if (section_type == SectionType::UNKNOWN) {
-      LOG(WARNING) << "Dropped an unknown section in SitesExploration list.";
+    if (section_type != SectionType::PERSONALIZED) {
       continue;
     }
     const base::ListValue* sites_list;
@@ -183,12 +183,6 @@ std::map<SectionType, PopularSites::SitesVector> ParseVersion6OrAbove(
     }
     sections[section_type] = ParseSiteList(*sites_list);
   }
-  if (!base::FeatureList::IsEnabled(kSiteExplorationUiFeature)) {
-    // New versions of popular sites that should act like old versions will
-    // mimic having only the personalized list.
-    return {std::make_pair(SectionType::PERSONALIZED,
-                           std::move(sections[SectionType::PERSONALIZED]))};
-  }
   return sections;
 }
 
@@ -268,12 +262,12 @@ PopularSitesImpl::PopularSitesImpl(
     const TemplateURLService* template_url_service,
     VariationsService* variations_service,
     scoped_refptr<network::SharedURLLoaderFactory> url_loader_factory,
-    ParseJSONCallback parse_json)
+    const ParseJSONCallback& parse_json)
     : prefs_(prefs),
       template_url_service_(template_url_service),
       variations_(variations_service),
       url_loader_factory_(std::move(url_loader_factory)),
-      parse_json_(std::move(parse_json)),
+      parse_json_(parse_json),
       is_fallback_(false),
       sections_(
           ParseSites(*prefs->GetList(prefs::kPopularSitesJsonPref),
@@ -450,11 +444,7 @@ void PopularSitesImpl::FetchPopularSites() {
         })");
   auto resource_request = std::make_unique<network::ResourceRequest>();
   resource_request->url = pending_url_;
-  resource_request->load_flags =
-      net::LOAD_DO_NOT_SEND_COOKIES | net::LOAD_DO_NOT_SAVE_COOKIES;
-  // TODO(https://crbug.com/808498): Re-add data use measurement once
-  // SimpleURLLoader supports it.
-  // ID=data_use_measurement::DataUseUserData::NTP_TILES
+  resource_request->allow_credentials = false;
   simple_url_loader_ = network::SimpleURLLoader::Create(
       std::move(resource_request), traffic_annotation);
   simple_url_loader_->SetRetryOptions(
@@ -475,15 +465,15 @@ void PopularSitesImpl::OnSimpleLoaderComplete(
   }
 
   parse_json_.Run(*response_body,
-                  base::Bind(&PopularSitesImpl::OnJsonParsed,
-                             weak_ptr_factory_.GetWeakPtr()),
-                  base::Bind(&PopularSitesImpl::OnJsonParseFailed,
-                             weak_ptr_factory_.GetWeakPtr()));
+                  base::BindOnce(&PopularSitesImpl::OnJsonParsed,
+                                 weak_ptr_factory_.GetWeakPtr()),
+                  base::BindOnce(&PopularSitesImpl::OnJsonParseFailed,
+                                 weak_ptr_factory_.GetWeakPtr()));
 }
 
-void PopularSitesImpl::OnJsonParsed(std::unique_ptr<base::Value> json) {
+void PopularSitesImpl::OnJsonParsed(base::Value json) {
   std::unique_ptr<base::ListValue> list =
-      base::ListValue::From(std::move(json));
+      base::ListValue::From(base::Value::ToUniquePtrValue(std::move(json)));
   if (!list) {
     DLOG(WARNING) << "JSON is not a list";
     OnDownloadFailed();
diff --git a/chromium/components/ntp_tiles/popular_sites_impl.h b/chromium/components/ntp_tiles/popular_sites_impl.h
index 43588d01250..5b51e289ccb 100644
--- a/chromium/components/ntp_tiles/popular_sites_impl.h
+++ b/chromium/components/ntp_tiles/popular_sites_impl.h
@@ -39,10 +39,10 @@ class TemplateURLService;
 
 namespace ntp_tiles {
 
-using ParseJSONCallback = base::Callback<void(
+using ParseJSONCallback = base::RepeatingCallback<void(
     const std::string& unsafe_json,
-    const base::Callback<void(std::unique_ptr<base::Value>)>& success_callback,
-    const base::Callback<void(const std::string&)>& error_callback)>;
+    base::OnceCallback<void(base::Value)> success_callback,
+    base::OnceCallback<void(const std::string&)> error_callback)>;
 
 // Actual (non-test) implementation of the PopularSites interface. Caches the
 // downloaded file on disk to avoid re-downloading on every startup.
@@ -53,7 +53,7 @@ class PopularSitesImpl : public PopularSites {
       const TemplateURLService* template_url_service,
       variations::VariationsService* variations_service,
       scoped_refptr<network::SharedURLLoaderFactory> url_loader_factory,
-      ParseJSONCallback parse_json);
+      const ParseJSONCallback& parse_json);
 
   ~PopularSitesImpl() override;
 
@@ -80,7 +80,7 @@ class PopularSitesImpl : public PopularSites {
   // Called once SimpleURLLoader completes the network request.
   void OnSimpleLoaderComplete(std::unique_ptr<std::string> response_body);
 
-  void OnJsonParsed(std::unique_ptr<base::Value> json);
+  void OnJsonParsed(base::Value json);
   void OnJsonParseFailed(const std::string& error_message);
   void OnDownloadFailed();
 
diff --git a/chromium/components/ntp_tiles/popular_sites_impl_unittest.cc b/chromium/components/ntp_tiles/popular_sites_impl_unittest.cc
index b3b88f61882..b965d6b611d 100644
--- a/chromium/components/ntp_tiles/popular_sites_impl_unittest.cc
+++ b/chromium/components/ntp_tiles/popular_sites_impl_unittest.cc
@@ -22,13 +22,13 @@
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/values.h"
 #include "build/build_config.h"
-#include "components/ntp_tiles/constants.h"
-#include "components/ntp_tiles/json_unsafe_parser.h"
+#include "components/ntp_tiles/features.h"
 #include "components/ntp_tiles/pref_names.h"
 #include "components/ntp_tiles/tile_source.h"
 #include "components/pref_registry/pref_registry_syncable.h"
 #include "components/sync_preferences/testing_pref_service_syncable.h"
 #include "net/http/http_status_code.h"
+#include "services/data_decoder/public/cpp/testing_json_parser.h"
 #include "services/network/public/cpp/shared_url_loader_factory.h"
 #include "services/network/public/cpp/weak_wrapper_shared_url_loader_factory.h"
 #include "services/network/test/test_url_loader_factory.h"
@@ -204,7 +204,7 @@ class PopularSitesTest : public ::testing::Test {
         prefs_.get(),
         /*template_url_service=*/nullptr,
         /*variations_service=*/nullptr, test_shared_loader_factory_,
-        base::Bind(JsonUnsafeParser::Parse));
+        base::Bind(&data_decoder::SafeJsonParser::Parse, nullptr));
   }
 
   const TestPopularSite kWikipedia;
@@ -213,6 +213,7 @@ class PopularSitesTest : public ::testing::Test {
 
   base::test::ScopedTaskEnvironment task_environment_{
       base::test::ScopedTaskEnvironment::MainThreadType::UI};
+  data_decoder::TestingJsonParser::ScopedFactoryOverride factory_override_;
   std::unique_ptr<sync_preferences::TestingPrefServiceSyncable> prefs_;
   network::TestURLLoaderFactory test_url_loader_factory_;
   scoped_refptr<network::SharedURLLoaderFactory> test_shared_loader_factory_;
@@ -531,10 +532,7 @@ TEST_F(PopularSitesTest, ShouldOverrideDirectory) {
   EXPECT_THAT(sites.size(), Eq(1u));
 }
 
-TEST_F(PopularSitesTest, DoesNotFetchExplorationSitesWithoutFeature) {
-  base::test::ScopedFeatureList override_features;
-  override_features.InitAndDisableFeature(kSiteExplorationUiFeature);
-
+TEST_F(PopularSitesTest, DoesNotFetchExplorationSites) {
   SetCountryAndVersion("ZZ", "6");
   RespondWithV6JSON(
       "https://www.gstatic.com/chrome/ntp/suggested_sites_ZZ_6.json",
@@ -549,46 +547,5 @@ TEST_F(PopularSitesTest, DoesNotFetchExplorationSitesWithoutFeature) {
   EXPECT_THAT(sections, Not(Contains(Pair(SectionType::NEWS, _))));
 }
 
-TEST_F(PopularSitesTest, FetchesExplorationSitesWithFeature) {
-  base::test::ScopedFeatureList override_features;
-  override_features.InitAndEnableFeature(kSiteExplorationUiFeature);
-  SetCountryAndVersion("ZZ", "6");
-  RespondWithV6JSON(
-      "https://www.gstatic.com/chrome/ntp/suggested_sites_ZZ_6.json",
-      {{SectionType::PERSONALIZED, {kChromium}},
-       {SectionType::ENTERTAINMENT, {kWikipedia, kYouTube}},
-       {SectionType::NEWS, {kYouTube}},
-       {SectionType::TOOLS, TestPopularSiteVector{}}});
-
-  std::map<SectionType, PopularSites::SitesVector> sections;
-  EXPECT_THAT(FetchAllSections(/*force_download=*/false, &sections),
-              Eq(base::Optional<bool>(true)));
-
-  EXPECT_THAT(sections, ElementsAre(Pair(SectionType::PERSONALIZED, SizeIs(1)),
-                                    Pair(SectionType::ENTERTAINMENT, SizeIs(2)),
-                                    Pair(SectionType::NEWS, SizeIs(1)),
-                                    Pair(SectionType::TOOLS, IsEmpty())));
-}
-
-TEST_F(PopularSitesTest, FetchesExplorationSitesIgnoreUnknownSections) {
-  base::test::ScopedFeatureList override_features;
-  override_features.InitAndEnableFeature(kSiteExplorationUiFeature);
-
-  SetCountryAndVersion("ZZ", "6");
-  RespondWithV6JSON(
-      "https://www.gstatic.com/chrome/ntp/suggested_sites_ZZ_6.json",
-      {{SectionType::UNKNOWN, {kChromium}},
-       {SectionType::NEWS, {kYouTube}},
-       {SectionType::UNKNOWN, {kWikipedia, kYouTube}}});
-
-  std::map<SectionType, PopularSites::SitesVector> sections;
-  EXPECT_THAT(FetchAllSections(/*force_download=*/false, &sections),
-              Eq(base::Optional<bool>(true)));
-
-  // Expect that there are four sections, none of which is empty.
-  EXPECT_THAT(sections, ElementsAre(Pair(SectionType::PERSONALIZED, SizeIs(0)),
-                                    Pair(SectionType::NEWS, SizeIs(1))));
-}
-
 }  // namespace
 }  // namespace ntp_tiles
diff --git a/chromium/components/ntp_tiles/tile_source.h b/chromium/components/ntp_tiles/tile_source.h
index 689411b4302..899e94c9f8c 100644
--- a/chromium/components/ntp_tiles/tile_source.h
+++ b/chromium/components/ntp_tiles/tile_source.h
@@ -26,6 +26,8 @@ enum class TileSource {
   WHITELIST,
   // Tile containing the user-set home page is replacing the home page button.
   HOMEPAGE,
+  // Tile comes from explore sites list.
+  EXPLORE,
   // Tile containing the Google Search page.
   SEARCH_PAGE,
 
diff --git a/chromium/components/ntp_tiles/webui/ntp_tiles_internals_message_handler.cc b/chromium/components/ntp_tiles/webui/ntp_tiles_internals_message_handler.cc
index fdbadcbc115..0ba8febaa8a 100644
--- a/chromium/components/ntp_tiles/webui/ntp_tiles_internals_message_handler.cc
+++ b/chromium/components/ntp_tiles/webui/ntp_tiles_internals_message_handler.cc
@@ -18,6 +18,7 @@
 #include "base/task_runner_util.h"
 #include "base/values.h"
 #include "components/favicon/core/favicon_service.h"
+#include "components/ntp_tiles/constants.h"
 #include "components/ntp_tiles/most_visited_sites.h"
 #include "components/ntp_tiles/pref_names.h"
 #include "components/ntp_tiles/webui/ntp_tiles_internals_message_handler_client.h"
@@ -58,9 +59,7 @@ NTPTilesInternalsMessageHandler::NTPTilesInternalsMessageHandler(
     favicon::FaviconService* favicon_service)
     : favicon_service_(favicon_service),
       client_(nullptr),
-      // 9 tiles are required for the custom links feature in order to balance
-      // the Most Visited rows (this is due to an additional "Add" button).
-      site_count_(9),
+      site_count_(ntp_tiles::kMaxNumMostVisited),
       weak_ptr_factory_(this) {}
 
 NTPTilesInternalsMessageHandler::~NTPTilesInternalsMessageHandler() = default;