ui: Cleanup class/struct forward declarations

ui/message_center/views/message_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 UI_MESSAGE_CENTER_VIEWS_MESSAGE_VIEW_H_
 #define UI_MESSAGE_CENTER_VIEWS_MESSAGE_VIEW_H_
 
 #include <memory>
 
 #include "base/macros.h"
 #include "base/strings/string16.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/gfx/geometry/insets.h"
 #include "ui/gfx/image/image.h"
 #include "ui/gfx/image/image_skia.h"
 #include "ui/message_center/message_center_export.h"
 #include "ui/message_center/notification.h"
 #include "ui/views/controls/button/button.h"
 #include "ui/views/controls/slide_out_view.h"
 
-namespace ui {
-class MenuModel;
-}
-
 namespace views {
 class ImageButton;
 class ImageView;
 class Painter;
 class ScrollView;
 }
 
 namespace message_center {
 
 class MessageCenterController;
@@ skipping 84 matching lines @@
   base::string16 display_source_;
 
   std::unique_ptr<views::Painter> focus_painter_;
 
   DISALLOW_COPY_AND_ASSIGN(MessageView);
 };
 
 }  // namespace message_center
 
 #endif // UI_MESSAGE_CENTER_VIEWS_MESSAGE_VIEW_H_