Update {virtual,override,final} to follow C++11 style in ash.

ash/system/chromeos/session/logout_button_tray.cc

 // 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.
 
 #include "ash/system/chromeos/session/logout_button_tray.h"
 
 #include "ash/shelf/shelf_types.h"
 #include "ash/shell.h"
 #include "ash/system/chromeos/session/logout_confirmation_controller.h"
 #include "ash/system/status_area_widget.h"
@@ skipping 38 matching lines @@
   IDR_AURA_UBER_TRAY_LOGOUT_BUTTON_PUSHED_CENTER,
   IDR_AURA_UBER_TRAY_LOGOUT_BUTTON_PUSHED_RIGHT,
   IDR_AURA_UBER_TRAY_LOGOUT_BUTTON_PUSHED_BOTTOM_LEFT,
   IDR_AURA_UBER_TRAY_LOGOUT_BUTTON_PUSHED_BOTTOM,
   IDR_AURA_UBER_TRAY_LOGOUT_BUTTON_PUSHED_BOTTOM_RIGHT
 };
 
 class LogoutButton : public views::LabelButton {
  public:
   LogoutButton(views::ButtonListener* listener);
-  virtual ~LogoutButton();
+  ~LogoutButton() override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(LogoutButton);
 };
 
 }  // namespace
 
 LogoutButton::LogoutButton(views::ButtonListener* listener)
     : views::LabelButton(listener, base::string16()) {
   SetupLabelForTray(label());
@@ skipping 86 matching lines @@
   UpdateVisibility();
 }
 
 void LogoutButtonTray::UpdateVisibility() {
   SetVisible(show_logout_button_in_tray_ &&
              login_status_ != user::LOGGED_IN_NONE &&
              login_status_ != user::LOGGED_IN_LOCKED);
 }
 
 }  // namespace ash