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

ash/system/tray/system_tray_item.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_TRAY_SYSTEM_TRAY_ITEM_H_
 #define ASH_SYSTEM_TRAY_SYSTEM_TRAY_ITEM_H_
 
 #include "ash/ash_export.h"
 #include "ash/system/user/login_status.h"
 #include "ash/wm/shelf_types.h"
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 
 namespace views {
 class View;
 }
 
 namespace ash {
 
+class SystemTray;
+
 namespace internal {
 class TrayItemView;
 }
 
 class ASH_EXPORT SystemTrayItem {
  public:
-  SystemTrayItem();
+  explicit SystemTrayItem(SystemTray* system_tray);
   virtual ~SystemTrayItem();
 
   // Create* functions may return NULL if nothing should be displayed for the
   // type of view. The default implementations return NULL.
 
   // Returns a view to be displayed in the system tray. If this returns NULL,
   // then this item is not displayed in the tray.
   // NOTE: The returned view should almost always be a TrayItemView, which
   // automatically resizes the widget when the size of the view changes, and
   // adds animation when the visibility of the view changes. If a view wants to
@@ skipping 56 matching lines @@
   // Shows a notification for this item.
   void ShowNotificationView();
 
   // Hides the notification for this item.
   void HideNotificationView();
 
   // Returns true if this item needs to force the launcher to be visible when
   // the launcher is in the auto-hide state. Default is true.
   virtual bool ShouldShowLauncher() const;
 
+  // Returns the system tray that this item belongs to.
+  SystemTray* system_tray() const { return system_tray_; }
+
  private:
+  SystemTray* system_tray_;
+
   DISALLOW_COPY_AND_ASSIGN(SystemTrayItem);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_TRAY_SYSTEM_TRAY_ITEM_H_