Remove #pragma once from ash

ash/system/drive/tray_drive.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_DRIVE_TRAY_DRIVE_H_
 #define ASH_SYSTEM_DRIVE_TRAY_DRIVE_H_
-#pragma once
 
 #include "ash/system/drive/drive_observer.h"
 #include "ash/system/tray/tray_image_item.h"
 
 namespace views {
 class Label;
 }
 
 namespace ash {
 
@@ skipping 33 matching lines @@
   tray::DriveDefaultView* default_;
   tray::DriveDetailedView* detailed_;
 
   DISALLOW_COPY_AND_ASSIGN(TrayDrive);
 };
 
 }  // namespace internal
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_DRIVE_TRAY_DRIVE_H_