Prepare SystemTray to support notifications

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"
-#include "base/memory/scoped_ptr.h"
 
 namespace ash {
 namespace internal {
 
 namespace tray {
 class VolumeView;
 }
 
 class TrayVolume : public TrayImageItem,
                    public AudioObserver {
  public:
   TrayVolume();
   virtual ~TrayVolume();
 
  private:
   // Overridden from TrayImageItem.
   virtual bool GetInitialVisibility() OVERRIDE;
 
   // Overridden from SystemTrayItem.
   virtual views::View* CreateDefaultView(user::LoginStatus status) OVERRIDE;
   virtual views::View* CreateDetailedView(user::LoginStatus status) OVERRIDE;
   virtual void DestroyDefaultView() OVERRIDE;
   virtual void DestroyDetailedView() OVERRIDE;
 
   // Overridden from AudioObserver.
   virtual void OnVolumeChanged(float percent) OVERRIDE;
 
-  scoped_ptr<tray::VolumeView> volume_view_;
+  tray::VolumeView* volume_view_;
 
   // Was |volume_view_| created for CreateDefaultView() rather than
   // CreateDetailedView()?  Used to avoid resetting |volume_view_|
   // 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_