ui: Cleanup class/struct forward declarations

ui/views/controls/menu/menu_message_loop_aura.h

 // Copyright 2014 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_VIEWS_CONTROLS_MENU_MENU_MESSAGE_LOOP_AURA_H_
 #define UI_VIEWS_CONTROLS_MENU_MENU_MESSAGE_LOOP_AURA_H_
 
 #include <memory>
 
 #include "base/callback.h"
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "ui/views/controls/menu/menu_message_loop.h"
 
-namespace ui {
-class ScopedEventDispatcher;
-}
-
 namespace views {
 
 class MenuMessageLoopAura : public MenuMessageLoop {
  public:
   MenuMessageLoopAura();
   ~MenuMessageLoopAura() override;
 
   // MenuMessageLoop:
   void Run() override;
   void QuitNow() override;
 
  private:
   base::Closure message_loop_quit_;
 
   DISALLOW_COPY_AND_ASSIGN(MenuMessageLoopAura);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_CONTROLS_MENU_MENU_MESSAGE_LOOP_AURA_H_