ui: Cleanup class/struct forward declarations

ui/views/controls/menu/menu_host.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_VIEWS_CONTROLS_MENU_MENU_HOST_H_
 #define UI_VIEWS_CONTROLS_MENU_MENU_HOST_H_
 
 #include <memory>
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/views/widget/widget.h"
 
 namespace views {
 
-class NativeWidget;
 class SubmenuView;
 class View;
 class Widget;
 
 namespace internal {
 
 // This class is internal to views.
 class PreMenuEventDispatchHandler;
 
 }  // internal
@@ skipping 64 matching lines @@
   // Handles raw touch events at the moment.
   std::unique_ptr<internal::PreMenuEventDispatchHandler> pre_dispatch_handler_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(MenuHost);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_CONTROLS_MENU_MENU_HOST_H_