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

ash/system/settings/tray_settings.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_SETTINGS_TRAY_SETTINGS_H_
 #define ASH_SYSTEM_SETTINGS_TRAY_SETTINGS_H_
 
 #include "ash/system/power/power_status_observer.h"
 #include "ash/system/tray/system_tray_item.h"
 
 namespace ash {
 namespace internal {
 
 namespace tray {
 class SettingsDefaultView;
 }
 
 class TraySettings : public SystemTrayItem,
                      public PowerStatusObserver {
  public:
-  TraySettings();
+  explicit TraySettings(SystemTray* system_tray);
   virtual ~TraySettings();
 
  private:
   // Overridden from SystemTrayItem
   virtual views::View* CreateTrayView(user::LoginStatus status) OVERRIDE;
   virtual views::View* CreateDefaultView(user::LoginStatus status) OVERRIDE;
   virtual views::View* CreateDetailedView(user::LoginStatus status) OVERRIDE;
   virtual void DestroyTrayView() OVERRIDE;
   virtual void DestroyDefaultView() OVERRIDE;
   virtual void DestroyDetailedView() OVERRIDE;
   virtual void UpdateAfterLoginStatusChange(user::LoginStatus status) OVERRIDE;
 
   // Overridden from PowerStatusObserver.
   virtual void OnPowerStatusChanged(const PowerSupplyStatus& status) OVERRIDE;
 
   tray::SettingsDefaultView* default_view_;
 
   DISALLOW_COPY_AND_ASSIGN(TraySettings);
 };
 
 }  // namespace internal
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_SETTINGS_TRAY_SETTINGS_H_