chrome: Cleanup class/struct forward declarations

chrome/browser/extensions/api/media_galleries/media_galleries_api.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.
 
 // Defines the Chrome Extensions Media Galleries API functions for accessing
 // user's media files, as specified in the extension API IDL.
 
 #ifndef CHROME_BROWSER_EXTENSIONS_API_MEDIA_GALLERIES_MEDIA_GALLERIES_API_H_
 #define CHROME_BROWSER_EXTENSIONS_API_MEDIA_GALLERIES_MEDIA_GALLERIES_API_H_
 
@@ skipping 13 matching lines @@
 #include "chrome/common/media_galleries/metadata_types.h"
 #include "components/storage_monitor/media_storage_util.h"
 #include "extensions/browser/browser_context_keyed_api_factory.h"
 #include "extensions/browser/event_router.h"
 #include "extensions/browser/extension_event_histogram_value.h"
 
 namespace MediaGalleries = extensions::api::media_galleries;
 
 namespace content {
 class BlobHandle;
-class WebContents;
-}
-
-namespace metadata {
-class SafeMediaMetadataParser;
 }
 
 namespace extensions {
 
-class Extension;
-
 // The profile-keyed service that manages the media galleries extension API.
 // Created at the same time as the Profile. This is also the event router.
 class MediaGalleriesEventRouter : public BrowserContextKeyedAPI,
                                   public GalleryWatchManagerObserver,
                                   public extensions::EventRouter::Observer {
  public:
   // KeyedService implementation.
   void Shutdown() override;
 
   // BrowserContextKeyedAPI implementation.
@@ skipping 167 matching lines @@
   ~MediaGalleriesRemoveGalleryWatchFunction() override;
   bool RunAsync() override;
 
  private:
   void OnPreferencesInit(const std::string& pref_id);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_MEDIA_GALLERIES_MEDIA_GALLERIES_API_H_