Stop using shell::GetInstance()->system_tray() in system tray items

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_
 
 #include "ash/system/audio/audio_observer.h"
 #include "ash/system/tray/tray_image_item.h"
 
 namespace ash {
 namespace internal {
 
 namespace tray {
 class VolumeView;
 }
 
 class TrayVolume : public TrayImageItem,
                    public AudioObserver {
  public:
-  TrayVolume();
+  explicit TrayVolume(SystemTray* system_tray);
   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;
@@ skipping 11 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_