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

ash/system/audio/tray_volume.cc

 // 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.
 
 #include "ash/system/audio/tray_volume.h"
 
 #include <cmath>
 
 #include "ash/ash_constants.h"
 #include "ash/shell.h"
@@ skipping 195 matching lines @@
 
   VolumeButton* icon_;
   MuteButton* mute_;
   VolumeSlider* slider_;
 
   DISALLOW_COPY_AND_ASSIGN(VolumeView);
 };
 
 }  // namespace tray
 
-TrayVolume::TrayVolume()
-    : TrayImageItem(IDR_AURA_UBER_TRAY_VOLUME_MUTE),
+TrayVolume::TrayVolume(SystemTray* system_tray)
+    : TrayImageItem(system_tray, IDR_AURA_UBER_TRAY_VOLUME_MUTE),
       volume_view_(NULL),
       is_default_view_(false) {
 }
 
 TrayVolume::~TrayVolume() {
 }
 
 bool TrayVolume::GetInitialVisibility() {
   return IsAudioMuted();
 }
@@ skipping 43 matching lines @@
       tray_view()->SetVisible(GetInitialVisibility());
 
   if (volume_view_)
     volume_view_->Update();
   else
     PopupDetailedView(kTrayPopupAutoCloseDelayInSeconds, false);
 }
 
 }  // namespace internal
 }  // namespace ash