Update chromeos system menu buttons for MD.

ash/common/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_COMMON_SYSTEM_USER_USER_VIEW_H_
 #define ASH_COMMON_SYSTEM_USER_USER_VIEW_H_
 
 #include <memory>
 
 #include "ash/common/session/session_types.h"
@@ skipping 56 matching lines @@
   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();
 
   // Removes the add user menu option.
   void RemoveAddUserMenuOption();
 
-  UserIndex user_index_;
-  // The view of the user card.
+  const UserIndex user_index_;
   views::View* user_card_view_;
 
   // This is the owner system tray item of this view.
   SystemTrayItem* owner_;
 
   // True if |user_card_view_| is a |ButtonFromView| - otherwise it is only
   // a |UserCardView|.
   bool is_user_card_button_;
 
   views::View* logout_button_;
   std::unique_ptr<PopupMessage> popup_message_;
   std::unique_ptr<views::Widget> add_menu_option_;
 
   // False when the add user panel is visible but not activatable.
   bool add_user_enabled_;
 
   // The mouse watcher which takes care of out of window hover events.
   std::unique_ptr<views::MouseWatcher> mouse_watcher_;
 
   // The focus manager which we use to detect focus changes.
   views::FocusManager* focus_manager_;
 
   DISALLOW_COPY_AND_ASSIGN(UserView);
 };
 
 }  // namespace tray
 }  // namespace ash
 
 #endif  // ASH_COMMON_SYSTEM_USER_USER_VIEW_H_