Remove #pragma once from ash

ash/system/user/tray_user.h

 // Copyright (c) 2012 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_TRAY_USER_H_
 #define ASH_SYSTEM_USER_TRAY_USER_H_
-#pragma once
 
 #include "ash/system/tray/system_tray_item.h"
 #include "ash/system/user/user_observer.h"
 
 namespace views {
 class ImageView;
 }
 
 namespace ash {
 namespace internal {
@@ skipping 25 matching lines @@
   tray::UserView* user_;
   tray::RoundedImageView* avatar_;
 
   DISALLOW_COPY_AND_ASSIGN(TrayUser);
 };
 
 }  // namespace internal
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_USER_TRAY_USER_H_