chrome: Cleanup class/struct forward declarations

chrome/browser/sync/glue/extension_setting_data_type_controller.h

 // Copyright (c) 2012 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_GLUE_EXTENSION_SETTING_DATA_TYPE_CONTROLLER_H__
 #define CHROME_BROWSER_SYNC_GLUE_EXTENSION_SETTING_DATA_TYPE_CONTROLLER_H__
 
 #include <string>
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "components/sync/driver/non_ui_data_type_controller.h"
 
 class Profile;
 
-namespace extensions {
-class StorageFrontend;
-}
-
 namespace syncer {
 class SyncClient;
 }
 
 namespace browser_sync {
 
 class ExtensionSettingDataTypeController
     : public syncer::NonUIDataTypeController {
  public:
   // |type| is either EXTENSION_SETTINGS or APP_SETTINGS.
@@ skipping 15 matching lines @@
 
   // Only used on the UI thread.
   Profile* profile_;
 
   DISALLOW_COPY_AND_ASSIGN(ExtensionSettingDataTypeController);
 };
 
 }  // namespace browser_sync
 
 #endif  // CHROME_BROWSER_SYNC_GLUE_EXTENSION_SETTING_DATA_TYPE_CONTROLLER_H__