chrome: Cleanup class/struct forward declarations

chrome/browser/media_galleries/media_galleries_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_MEDIA_GALLERIES_MEDIA_GALLERIES_PREFERENCES_H_
 #define CHROME_BROWSER_MEDIA_GALLERIES_MEDIA_GALLERIES_PREFERENCES_H_
 
 #include <stdint.h>
 
 #include <map>
 #include <set>
 #include <string>
 #include <vector>
 
 #include "base/callback_forward.h"
 #include "base/files/file_path.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/observer_list.h"
 #include "base/strings/string16.h"
 #include "base/time/time.h"
 #include "components/keyed_service/core/keyed_service.h"
 #include "components/storage_monitor/removable_storage_observer.h"
 
 class Profile;
 
-namespace base {
-class DictionaryValue;
-}
-
 namespace extensions {
 class Extension;
 class ExtensionPrefs;
 }
 
 namespace user_prefs {
 class PrefRegistrySyncable;
 }
 
 typedef uint64_t MediaGalleryPrefId;
@@ skipping 348 matching lines @@
   DeviceIdPrefIdsMap device_map_;
 
   base::ObserverList<GalleryChangeObserver> gallery_change_observers_;
 
   base::WeakPtrFactory<MediaGalleriesPreferences> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(MediaGalleriesPreferences);
 };
 
 #endif  // CHROME_BROWSER_MEDIA_GALLERIES_MEDIA_GALLERIES_PREFERENCES_H_