ui: Cleanup class/struct forward declarations

ui/views/controls/menu/menu_separator.h

 // Copyright (c) 2011 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_SEPARATOR_H_
 #define UI_VIEWS_CONTROLS_MENU_MENU_SEPARATOR_H_
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "ui/base/models/menu_separator_types.h"
 #include "ui/views/view.h"
 
 namespace views {
 
-class MenuItemView;
-
 class MenuSeparator : public View {
  public:
   explicit MenuSeparator(ui::MenuSeparatorType type) : type_(type) {}
 
   // View overrides.
   void OnPaint(gfx::Canvas* canvas) override;
   gfx::Size GetPreferredSize() const override;
 
  private:
   // Gets the bounds where the separator should be painted.
   gfx::Rect GetPaintBounds();
 
   void OnPaintAura(gfx::Canvas* canvas);
 
   // The type of the separator.
   const ui::MenuSeparatorType type_;
 
   DISALLOW_COPY_AND_ASSIGN(MenuSeparator);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_CONTROLS_MENU_MENU_SEPARATOR_H_