Replace ButtonDropDown menu implementation (Menu2) with MenuItemView.

views/controls/menu/menu_item_view.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 VIEWS_CONTROLS_MENU_MENU_ITEM_VIEW_H_
 #define VIEWS_CONTROLS_MENU_MENU_ITEM_VIEW_H_
 #pragma once
 
 #include <string>
 #include <vector>
@@ skipping 61 matching lines @@
 
   // The menu item view's class name.
   static const char kViewClassName[];
 
   // ID used to identify menu items.
   static const int kMenuItemViewID;
 
   // ID used to identify empty menu items.
   static const int kEmptyMenuItemViewID;
 
-  // Different types of menu items.
+  // Different types of menu items.  EMPTY is a special type for empty
+  // menus that is only used internally.
   enum Type {
     NORMAL,
     SUBMENU,
     CHECKBOX,
     RADIO,
-    SEPARATOR
+    SEPARATOR,
+    EMPTY
   };
 
   // Where the menu should be anchored to.
   enum AnchorPosition {
     TOPLEFT,
     TOPRIGHT
   };
 
   // Constructor for use with the top level menu item. This menu is never
   // shown to the user, rather its use as the parent for all menu items.
@@ skipping 359 matching lines @@
   // Margins in pixels.
   int top_margin_;
   int bottom_margin_;
 
   DISALLOW_COPY_AND_ASSIGN(MenuItemView);
 };
 
 }  // namespace views
 
 #endif  // VIEWS_CONTROLS_MENU_MENU_ITEM_VIEW_H_