chrome: Cleanup class/struct forward declarations

chrome/browser/chromeos/preferences.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_CHROMEOS_PREFERENCES_H_
 #define CHROME_BROWSER_CHROMEOS_PREFERENCES_H_
 
 #include <string>
 
 #include "ash/common/shell_observer.h"
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "chrome/browser/chromeos/language_preferences.h"
 #include "components/prefs/pref_change_registrar.h"
 #include "components/prefs/pref_member.h"
 #include "components/sync_preferences/pref_service_syncable_observer.h"
 #include "components/user_manager/user_manager.h"
 #include "ui/base/ime/chromeos/input_method_manager.h"
 
 class PrefRegistrySimple;
-class PrefService;
 class TracingManager;
 
 namespace sync_preferences {
 class PrefServiceSyncable;
 }
 
 namespace user_prefs {
 class PrefRegistrySyncable;
 }
 
@@ skipping 127 matching lines @@
   scoped_refptr<input_method::InputMethodManager::State> ime_state_;
 
   std::unique_ptr<input_method::InputMethodSyncer> input_method_syncer_;
 
   DISALLOW_COPY_AND_ASSIGN(Preferences);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_PREFERENCES_H_