ash: Cleanup class/struct forward declarations

ash/common/system/tray/tray_notification_view.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 ASH_COMMON_SYSTEM_TRAY_TRAY_NOTIFICATION_VIEW_H_
 #define ASH_COMMON_SYSTEM_TRAY_TRAY_NOTIFICATION_VIEW_H_
 
 #include "base/macros.h"
 #include "base/timer/timer.h"
 #include "ui/views/controls/button/image_button.h"
 #include "ui/views/controls/slide_out_view.h"
 
-namespace gfx {
-class ImageSkia;
-}
-
 namespace views {
 class ImageView;
 }
 
 namespace ash {
 class SystemTrayItem;
 
 // A view for closable notification views, laid out like:
 //  -------------------
 // | icon  contents  x |
@@ skipping 47 matching lines @@
 
   int autoclose_delay_;
   base::OneShotTimer autoclose_;
 
   DISALLOW_COPY_AND_ASSIGN(TrayNotificationView);
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_SYSTEM_TRAY_TRAY_NOTIFICATION_VIEW_H_