[Sync] Move some code into new class JsMutationEventObserver

chrome/browser/sync/js/js_transaction_observer.h

-// 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.
-
-#ifndef CHROME_BROWSER_SYNC_JS_JS_TRANSACTION_OBSERVER_H_
-#define CHROME_BROWSER_SYNC_JS_JS_TRANSACTION_OBSERVER_H_
-#pragma once
-
-#include <string>
-
-#include "base/basictypes.h"
-#include "base/compiler_specific.h"
-#include "base/threading/non_thread_safe.h"
-#include "chrome/browser/sync/syncable/transaction_observer.h"
-#include "chrome/browser/sync/util/weak_handle.h"
-
-namespace tracked_objects {
-class Location;
-}  // namespace tracked_objects
-
-namespace browser_sync {
-
-class JsEventDetails;
-class JsEventHandler;
-
-// Routes SyncManager events to a JsEventHandler.
-class JsTransactionObserver : public syncable::TransactionObserver {
- public:
-  JsTransactionObserver();
-
-  virtual ~JsTransactionObserver();
-
-  void SetJsEventHandler(const WeakHandle<JsEventHandler>& event_handler);
-
-  // syncable::TransactionObserver implementation.
-  virtual void OnTransactionStart(
-      const tracked_objects::Location& location,
-      const syncable::WriterTag& writer) OVERRIDE;
-  virtual void OnTransactionWrite(
-      const syncable::ImmutableWriteTransactionInfo& write_transaction_info,
-      const syncable::ModelTypeBitSet& models_with_changes) OVERRIDE;
-  virtual void OnTransactionEnd(
-      const tracked_objects::Location& location,
-      const syncable::WriterTag& writer) OVERRIDE;
-
- private:
-  base::NonThreadSafe non_thread_safe_;
-  WeakHandle<JsEventHandler> event_handler_;
-
-  void HandleJsEvent(
-    const tracked_objects::Location& from_here,
-    const std::string& name, const JsEventDetails& details);
-
-  DISALLOW_COPY_AND_ASSIGN(JsTransactionObserver);
-};
-
-}  // namespace browser_sync
-
-#endif  // CHROME_BROWSER_SYNC_JS_JS_TRANSACTION_OBSERVER_H_