Remove dispatcher when shutting down RootWindowController

ash/root_window_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/root_window_controller.h"
 
 #include <queue>
 #include <vector>
 
 #include "ash/ash_constants.h"
@@ skipping 405 matching lines @@
   }
 
   CloseChildWindows();
   GetRootWindowSettings(root_window)->controller = NULL;
   screen_dimmer_.reset();
   workspace_controller_.reset();
   // Forget with the display ID so that display lookup
   // ends up with invalid display.
   GetRootWindowSettings(root_window)->display_id =
       gfx::Display::kInvalidDisplayID;
-  GetRootWindowSettings(root_window)->shutdown = true;
+  ash_host_->PrepareForShutdown();
 
   system_background_.reset();
   aura::client::SetScreenPositionClient(root_window, NULL);
 }
 
 SystemModalContainerLayoutManager*
 RootWindowController::GetSystemModalLayoutManager(aura::Window* window) {
   aura::Window* modal_container = NULL;
   if (window) {
     aura::Window* window_container = GetContainerForWindow(window);
@@ skipping 660 matching lines @@
   else
     DisableTouchHudProjection();
 }
 
 RootWindowController* GetRootWindowController(
     const aura::Window* root_window) {
   return root_window ? GetRootWindowSettings(root_window)->controller : NULL;
 }
 
 }  // namespace ash