Forget about DesktopBackgroundWidget if it was deleted

ash/desktop_background/desktop_background_controller.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_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_CONTROLLER_H_
 #define ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_CONTROLLER_H_
 
 #include "ash/ash_export.h"
 #include "ash/desktop_background/desktop_background_resources.h"
 #include "ash/wm/window_animations.h"
@@ skipping 107 matching lines @@
 
   // Returns the appropriate wallpaper resolution for all root windows.
   WallpaperResolution GetAppropriateResolution();
 
   // Move all desktop widgets to locked container.
   void MoveDesktopToLockedContainer();
 
   // Move all desktop widgets to unlocked container.
   void MoveDesktopToUnlockedContainer();
 
+  // Drop references to background view for |root_window|, because the view
+  // was deleted.
+  void CleanupView(aura::RootWindow* root_window);
+
   // WindowObserver implementation.
   virtual void OnWindowDestroying(aura::Window* window) OVERRIDE;
 
  private:
   // An operation to asynchronously loads wallpaper.
   class WallpaperOperation;
 
   struct WallpaperData;
 
   // Creates view for all root windows, or notifies them to repaint if they
@@ skipping 40 matching lines @@
   scoped_refptr<WallpaperOperation> wallpaper_op_;
 
   base::WeakPtrFactory<DesktopBackgroundController> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(DesktopBackgroundController);
 };
 
 }  // namespace ash
 
 #endif  // ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_CONTROLLER_H_