Forget about DesktopBackgroundWidget if it was deleted

ash/desktop_background/desktop_background_widget_controller.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/desktop_background/desktop_background_widget_controller.h"
 
 #include "ui/aura/root_window.h"
 #include "ui/views/widget/widget.h"
 
 DECLARE_WINDOW_PROPERTY_TYPE(ash::internal::DesktopBackgroundWidgetController*);
@@ skipping 16 matching lines @@
 }
 
 DesktopBackgroundWidgetController::~DesktopBackgroundWidgetController() {
   if (widget_) {
     widget_->CloseNow();
     widget_ = NULL;
   } else if (layer_.get())
     layer_.reset(NULL);
 }
 
+void DesktopBackgroundWidgetController::CleanupWidget() {
+  widget_ = NULL;
+}
+
 void DesktopBackgroundWidgetController::SetBounds(gfx::Rect bounds) {
   if (widget_)
     widget_->SetBounds(bounds);
   else if (layer_.get())
     layer_->SetBounds(bounds);
 }
 
 void DesktopBackgroundWidgetController::Reparent(aura::RootWindow* root_window,
                                                  int src_container,
                                                  int dest_container) {
@@ skipping 17 matching lines @@
 
 DesktopBackgroundWidgetController* ComponentWrapper::GetComponent(
     bool pass_ownership) {
   if (pass_ownership)
     return component_.release();
   return component_.get();
 }
 
 }  // namespace internal
 }  // namespace ash