Remove #pragma once from ash

ash/system/audio/tray_volume.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_AUDIO_TRAY_VOLUME_H_
 #define ASH_SYSTEM_AUDIO_TRAY_VOLUME_H_
-#pragma once
 
 #include "ash/system/audio/audio_observer.h"
 #include "ash/system/tray/tray_image_item.h"
 
 namespace ash {
 namespace internal {
 
 namespace tray {
 class VolumeView;
 }
@@ skipping 24 matching lines @@
   // inappropriately in DestroyDefaultView() or DestroyDetailedView().
   bool is_default_view_;
 
   DISALLOW_COPY_AND_ASSIGN(TrayVolume);
 };
 
 }  // namespace internal
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_AUDIO_TRAY_VOLUME_H_