1 files changed, 147 insertions, 0 deletions
diff --git a/chromium/third_party/blink/renderer/platform/wtf/text/movable_string.cc b/chromium/third_party/blink/renderer/platform/wtf/text/movable_string.cc
new file mode 100644
index 00000000000..fdfa440ea96
--- /dev/null
+++ b/chromium/third_party/blink/renderer/platform/wtf/text/movable_string.cc
@@ -0,0 +1,147 @@
+// Copyright 2018 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/platform/wtf/text/movable_string.h"
+
+#include "base/metrics/histogram_macros.h"
+
+namespace WTF {
+
+namespace {
+
+bool IsLargeEnough(const StringImpl* impl) {
+  // Don't attempt to park strings smaller than this size.
+  static constexpr unsigned int kSizeThreshold = 10000;
+  return impl && impl->length() > kSizeThreshold;
+}
+
+void RecordParkingAction(MovableStringImpl::ParkingAction action) {
+  UMA_HISTOGRAM_ENUMERATION("Memory.MovableStringParkingAction", action);
+}
+
+}  // namespace
+
+MovableStringImpl::MovableStringImpl() = default;
+
+MovableStringImpl::MovableStringImpl(scoped_refptr<StringImpl>&& impl)
+    : string_(std::move(impl)), is_parked_(false) {}
+
+MovableStringImpl::~MovableStringImpl() {
+  MovableStringTable::Instance().Remove(string_.Impl());
+}
+
+bool MovableStringImpl::Is8Bit() const {
+  return string_.Is8Bit();
+}
+
+bool MovableStringImpl::IsNull() const {
+  return string_.IsNull();
+}
+
+const String& MovableStringImpl::ToString() {
+  Unpark();
+  return string_;
+}
+
+unsigned MovableStringImpl::CharactersSizeInBytes() const {
+  return string_.CharactersSizeInBytes();
+}
+
+bool MovableStringImpl::Park() {
+  // Cannot park strings with several references.
+  if (string_.Impl()->HasOneRef()) {
+    RecordParkingAction(ParkingAction::kParkedInBackground);
+    is_parked_ = true;
+  }
+  return is_parked_;
+}
+
+void MovableStringImpl::Unpark() {
+  if (!is_parked_)
+    return;
+
+  bool backgrounded = MovableStringTable::Instance().IsRendererBackgrounded();
+  RecordParkingAction(backgrounded ? ParkingAction::kUnparkedInBackground
+                                   : ParkingAction::kUnparkedInForeground);
+  is_parked_ = false;
+}
+
+MovableString::MovableString(scoped_refptr<StringImpl>&& impl) {
+  // Don't move small strings.
+  if (IsLargeEnough(impl.get())) {
+    impl_ = MovableStringTable::Instance().Add(std::move(impl));
+  } else {
+    impl_ = base::MakeRefCounted<MovableStringImpl>(std::move(impl));
+  }
+}
+
+MovableString::~MovableString() = default;
+
+bool MovableString::Is8Bit() const {
+  return impl_->Is8Bit();
+}
+
+bool MovableString::IsNull() const {
+  return impl_->IsNull();
+}
+const String& MovableString::ToString() const {
+  return impl_->ToString();
+}
+
+unsigned MovableString::CharactersSizeInBytes() const {
+  return impl_->CharactersSizeInBytes();
+}
+
+MovableStringTable::MovableStringTable() = default;
+MovableStringTable::~MovableStringTable() = default;
+
+scoped_refptr<MovableStringImpl> MovableStringTable::Add(
+    scoped_refptr<StringImpl>&& string) {
+  StringImpl* raw_ptr = string.get();
+  auto it = table_.find(raw_ptr);
+  if (it != table_.end()) {
+    return it->second;
+  }
+  auto new_movable_string =
+      base::MakeRefCounted<MovableStringImpl>(std::move(string));
+  table_.emplace(raw_ptr, new_movable_string.get());
+  return new_movable_string;
+}
+
+void MovableStringTable::Remove(StringImpl* string) {
+  if (!IsLargeEnough(string))
+    return;
+
+  auto it = table_.find(string);
+  DCHECK(it != table_.end());
+  table_.erase(it);
+}
+
+void MovableStringTable::SetRendererBackgrounded(bool backgrounded) {
+  backgrounded_ = backgrounded;
+}
+
+bool MovableStringTable::IsRendererBackgrounded() const {
+  return backgrounded_;
+}
+
+void MovableStringTable::MaybeParkAll() {
+  if (!IsRendererBackgrounded())
+    return;
+
+  size_t total_size = 0, count = 0;
+  for (auto& kv : table_) {
+    MovableStringImpl* str = kv.second;
+    str->Park();
+    total_size += str->CharactersSizeInBytes();
+    count += 1;
+  }
+
+  size_t total_size_kb = total_size / 1000;
+  UMA_HISTOGRAM_COUNTS_100000("Memory.MovableStringsTotalSizeKb",
+                              total_size_kb);
+  UMA_HISTOGRAM_COUNTS_1000("Memory.MovableStringsCount", table_.size());
+}
+
+}  // namespace WTF