Forget about DesktopBackgroundWidget if it was deleted

ash/desktop_background/desktop_background_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_controller.h"
 
 #include "ash/desktop_background/desktop_background_view.h"
 #include "ash/desktop_background/desktop_background_widget_controller.h"
 #include "ash/shell.h"
 #include "ash/shell_factory.h"
@@ skipping 228 matching lines @@
 }
 
 void DesktopBackgroundController::MoveDesktopToLockedContainer() {
   if (locked_)
     return;
   locked_ = true;
   ReparentBackgroundWidgets(GetBackgroundContainerId(false),
                             GetBackgroundContainerId(true));
 }
 
+void DesktopBackgroundController::CleanupView(aura::RootWindow* root_window) {
+  internal::ComponentWrapper *wrapper;
+  wrapper = root_window->GetProperty(internal::kComponentWrapper);
+  if (NULL == wrapper)
+    return;
+  if (wrapper->GetComponent(false))
+    wrapper->GetComponent(false)->CleanupWidget();
+}
+
+
 void DesktopBackgroundController::MoveDesktopToUnlockedContainer() {
   if (!locked_)
     return;
   locked_ = false;
   ReparentBackgroundWidgets(GetBackgroundContainerId(true),
                             GetBackgroundContainerId(false));
 }
 
 void DesktopBackgroundController::OnWindowDestroying(aura::Window* window) {
   window->SetProperty(internal::kWindowDesktopComponent,
@@ skipping 100 matching lines @@
     }
   }
 }
 
 int DesktopBackgroundController::GetBackgroundContainerId(bool locked) {
   return locked ? internal::kShellWindowId_LockScreenBackgroundContainer :
                   internal::kShellWindowId_DesktopBackgroundContainer;
 }
 
 }  // namespace ash