Add onChanged events to the extension settings API, both from sync and between

chrome/browser/extensions/extension_settings_observer.cc

+// Copyright (c) 2011 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 "chrome/browser/extensions/extension_settings_observer.h"
+
+#include "base/json/json_writer.h"
+
+ExtensionSettingsObserver::ChangeList::ChangeList() {}
+
+ExtensionSettingsObserver::ChangeList::~ChangeList() {}
+
+void ExtensionSettingsObserver::ChangeList::AppendChange(
+    const std::string& key, Value* old_value, Value* new_value) {
+  DictionaryValue* change = new DictionaryValue();
+  change->Set("key", Value::CreateStringValue(key));
+  if (old_value) {
+    change->Set("oldValue", old_value);
+  }
+  if (new_value) {
+    change->Set("newValue", new_value);
+  }
+  changes_.Append(change);
+}
+
+std::string ExtensionSettingsObserver::ChangeList::GetEventJson() const {
+  std::string event_json;
+  base::JSONWriter::Write(&changes_, false, &event_json);
+  // Event JSON is a list of arguments to the onChanged callback, a singleton
+  // list of a list of changes.
+  return std::string("[") + event_json + "]";
+}
+
+ExtensionSettingsObserver::~ExtensionSettingsObserver() {}