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 0bd8b3542efdffc1fbf6f4ec800ef6d77c570ab8..bdbad059050002aff5d767ed9243a0b0d30f8769 100644
--- a/ash/desktop_background/desktop_background_controller.cc
+++ b/ash/desktop_background/desktop_background_controller.cc
@@ -246,6 +246,16 @@ 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;
+  if (wrapper->GetComponent(false))
+    wrapper->GetComponent(false)->CleanupWidget();
+}
+
+
 void DesktopBackgroundController::MoveDesktopToUnlockedContainer() {
   if (!locked_)
     return;