Revert 258077 "Remove PrepareForShutdown"

trunk/src/ui/aura/window_tree_host.h

 // 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.
 
 #ifndef UI_AURA_WINDOW_TREE_HOST_H_
 #define UI_AURA_WINDOW_TREE_HOST_H_
 
 #include <vector>
 
 #include "base/event_types.h"
@@ skipping 145 matching lines @@
   // being used in fullscreen mode, so root_window bounds = window bounds.
   virtual bool ConfineCursorToRootWindow() = 0;
   virtual void UnConfineCursor() = 0;
 
   // Posts |native_event| to the platform's event queue.
   virtual void PostNativeEvent(const base::NativeEvent& native_event) = 0;
 
   // Called when the device scale factor of the root window has chagned.
   virtual void OnDeviceScaleFactorChanged(float device_scale_factor) = 0;
 
+  // Stop listening events in preparation for shutdown.
+  virtual void PrepareForShutdown() = 0;
+
  protected:
   friend class TestScreen;  // TODO(beng): see if we can remove/consolidate.
 
   WindowTreeHost();
   void DestroyCompositor();
   void DestroyDispatcher();
 
   void CreateCompositor(gfx::AcceleratedWidget accelerated_widget);
 
   // Returns the location of the RootWindow on native screen.
@@ skipping 38 matching lines @@
   gfx::NativeCursor last_cursor_;
 
   scoped_ptr<ui::ViewProp> prop_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowTreeHost);
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_WINDOW_TREE_HOST_H_