fix build after clang roll

chrome/browser/sync_file_system/drive_backend/sync_engine.h

 // Copyright 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_SYNC_FILE_SYSTEM_DRIVE_BACKEND_SYNC_ENGINE_H_
 #define CHROME_BROWSER_SYNC_FILE_SYSTEM_DRIVE_BACKEND_SYNC_ENGINE_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "base/observer_list.h"
@@ skipping 122 matching lines @@
   // The owner of the SyncEngine is responsible for their lifetime.
   // I.e. the owner should declare the dependency explicitly by calling
   // BrowserContextKeyedService::DependsOn().
   drive::DriveNotificationManager* notification_manager_;
   ExtensionService* extension_service_;
 
   ObserverList<SyncServiceObserver> service_observers_;
   ObserverList<FileStatusObserver> file_status_observers_;
   RemoteChangeProcessor* remote_change_processor_;
 
+  // TODO: This should be the last member in this class.
+  base::WeakPtrFactory<SyncEngine> weak_ptr_factory_;
   SyncTaskManager task_manager_;
-  base::WeakPtrFactory<SyncEngine> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncEngine);
 };
 
 }  // namespace drive_backend
 }  // namespace sync_file_system
 
 #endif  // CHROME_BROWSER_SYNC_FILE_SYSTEM_DRIVE_BACKEND_SYNC_ENGINE_H_