chrome: Cleanup class/struct forward declarations

chrome/browser/bookmarks/startup_task_runner_service_factory.h

 // Copyright (c) 2013 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_BOOKMARKS_STARTUP_TASK_RUNNER_SERVICE_FACTORY_H_
 #define CHROME_BROWSER_BOOKMARKS_STARTUP_TASK_RUNNER_SERVICE_FACTORY_H_
 
 #include "base/macros.h"
 #include "base/memory/singleton.h"
 #include "components/keyed_service/content/browser_context_keyed_service_factory.h"
 
-class PrefRegistrySyncable;
 class Profile;
 
 namespace bookmarks {
 class StartupTaskRunnerService;
 }
 
 // Singleton that owns the start-up task runner service.
 class StartupTaskRunnerServiceFactory
     : public BrowserContextKeyedServiceFactory {
  public:
@@ skipping 11 matching lines @@
   ~StartupTaskRunnerServiceFactory() override;
 
   // BrowserContextKeyedServiceFactory:
   KeyedService* BuildServiceInstanceFor(
       content::BrowserContext* profile) const override;
 
   DISALLOW_COPY_AND_ASSIGN(StartupTaskRunnerServiceFactory);
 };
 
 #endif  // CHROME_BROWSER_BOOKMARKS_STARTUP_TASK_RUNNER_SERVICE_FACTORY_H_