Merge the tonic layer from skydart branch back to master

sky/engine/tonic/dart_string_cache.cc

+// Copyright 2014 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 "sky/engine/config.h"
+#include "sky/engine/tonic/dart_string_cache.h"
+
+#include "sky/engine/tonic/dart_state.h"
+#include "sky/engine/tonic/dart_string.h"
+
+namespace blink {
+
+DartStringCache::DartStringCache() : last_dart_string_(nullptr) {
+}
+
+DartStringCache::~DartStringCache() {
+}
+
+Dart_WeakPersistentHandle DartStringCache::GetSlow(StringImpl* string_impl,
+                                                   bool auto_scope) {
+  if (Dart_WeakPersistentHandle string = cache_.get(string_impl)) {
+    last_dart_string_ = string;
+    last_string_impl_ = string_impl;
+    return string;
+  }
+
+  if (!auto_scope)
+    Dart_EnterScope();
+
+  Dart_Handle string = CreateDartString(string_impl);
+  DCHECK(!Dart_IsError(string));
+
+  intptr_t size_in_bytes = string_impl->sizeInBytes();
+  Dart_WeakPersistentHandle wrapper = Dart_NewWeakPersistentHandle(
+      string, string_impl, size_in_bytes, FinalizeCacheEntry);
+
+  string_impl->ref();  // Balanced in FinalizeCacheEntry.
+  cache_.set(string_impl, wrapper);
+
+  last_dart_string_ = wrapper;
+  last_string_impl_ = string_impl;
+
+  if (!auto_scope)
+    Dart_ExitScope();
+
+  return wrapper;
+}
+
+void DartStringCache::FinalizeCacheEntry(void* isolate_callback_data,
+                                         Dart_WeakPersistentHandle handle,
+                                         void* peer) {
+  DartState* state = reinterpret_cast<DartState*>(isolate_callback_data);
+  StringImpl* string_impl = reinterpret_cast<StringImpl*>(peer);
+  DartStringCache& cache = state->string_cache();
+
+  Dart_WeakPersistentHandle cached_handle = cache.cache_.take(string_impl);
+  ASSERT_UNUSED(cached_handle, handle == cached_handle);
+
+  if (cache.last_dart_string_ == handle) {
+    cache.last_dart_string_ = nullptr;
+    cache.last_string_impl_ = nullptr;
+  }
+
+  string_impl->deref();
+}
+
+}  // namespace blink