Introduce a type of View background that stays in sync with its host

ash/system/user/user_view.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 ASH_SYSTEM_USER_USER_VIEW_H_
 #define ASH_SYSTEM_USER_USER_VIEW_H_
 
 #include <memory>
 
 #include "ash/public/cpp/session_types.h"
@@ skipping 44 matching lines @@
 
   // Overridden from views::FocusChangeListener:
   void OnWillChangeFocus(View* focused_before, View* focused_now) override;
   void OnDidChangeFocus(View* focused_before, View* focused_now) override;
 
   void AddLogoutButton(LoginStatus login);
   void AddUserCard(LoginStatus login);
 
   // Create the menu option to add another user. If |disabled| is set the user
   // cannot actively click on the item.
-  void ToggleAddUserMenuOption();
+  void ToggleUserDropdownWidget();
 
   // Removes the add user menu option.
-  void RemoveAddUserMenuOption();
+  void HideUserDropdownWidget();
 
   // If |user_card_view_| is clickable, this is a ButtonFromView that wraps it.
   // If |user_card_view_| is not clickable, this will be equal to
   // |user_card_view_|.
   views::View* user_card_container_ = nullptr;
 
   // The |UserCardView| for the active user.
   UserCardView* user_card_view_ = nullptr;
 
   // This is the owner system tray item of this view.
   SystemTrayItem* owner_;
 
   views::View* logout_button_ = nullptr;
-  std::unique_ptr<views::Widget> add_menu_option_;
+  std::unique_ptr<views::Widget> user_dropdown_widget_;
 
   // False when the add user panel is visible but not activatable.
   bool add_user_enabled_ = true;
 
   // The focus manager which we use to detect focus changes.
   views::FocusManager* focus_manager_ = nullptr;
 
   DISALLOW_COPY_AND_ASSIGN(UserView);
 };
 
 }  // namespace tray
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_USER_USER_VIEW_H_