Forget about DesktopBackgroundWidget if it was deleted

ash/desktop_background/desktop_background_controller.cc

Index: ash/desktop_background/desktop_background_controller.cc
diff --git a/ash/desktop_background/desktop_background_controller.cc b/ash/desktop_background/desktop_background_controller.cc
index 83b486c4808ea4692a786d0f352ccc178be46ea8..3324e38f595d8e0edcdce4ae5cea72434f2f6053 100644
--- a/ash/desktop_background/desktop_background_controller.cc
+++ b/ash/desktop_background/desktop_background_controller.cc
@@ -243,6 +243,15 @@ void DesktopBackgroundController::MoveDesktopToLockedContainer() {
                             GetBackgroundContainerId(true));
 }
 
+void DesktopBackgroundController::CleanUpView(aura::RootWindow* root_window) {
+  internal::ComponentWrapper *wrapper;
+  wrapper = root_window->GetProperty(internal::kComponentWrapper);
+  if (NULL == wrapper)
+    return;
+  wrapper->GetComponent(false)->CleanUpWidget();
+}
+
+
 void DesktopBackgroundController::MoveDesktopToUnlockedContainer() {
   if (!locked_)
     return;