Fix two crash and potential leak&crash

ash/accelerators/accelerator_dispatcher.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 ASH_ACCELERATORS_ACCELERATOR_DISPATCHER_H_
 #define ASH_ACCELERATORS_ACCELERATOR_DISPATCHER_H_
 #pragma once
 
 #include "ash/ash_export.h"
 #include "base/message_loop.h"
 #include "ui/aura/window.h"
+#include "ui/aura/window_observer.h"
 
 namespace ash {
 
 // Dispatcher for handling accelerators in ash.
 // Wraps a nested dispatcher to which control is passed if no accelerator key
 // has been pressed.
 // TODO(pkotwicz): Port AcceleratorDispatcher to mac.
-class ASH_EXPORT AcceleratorDispatcher : public MessageLoop::Dispatcher {
+class ASH_EXPORT AcceleratorDispatcher : public MessageLoop::Dispatcher,
+                                         public aura::WindowObserver {
  public:
   explicit AcceleratorDispatcher(MessageLoop::Dispatcher* nested_dispatcher,
                                  aura::Window* associated_window);
+  virtual ~AcceleratorDispatcher();
 
 #if defined(USE_X11)
   virtual base::MessagePumpDispatcher::DispatchStatus Dispatch(
       XEvent* xev) OVERRIDE;
 #elif defined(OS_WIN)
   bool AcceleratorDispatcher::Dispatch(const MSG& msg) OVERRIDE;
 #endif
 
+  // aura::WindowObserver overrides:
+  virtual void OnWindowDestroying(aura::Window* window) OVERRIDE;
+
  private:
   MessageLoop::Dispatcher* nested_dispatcher_;
 
   // Window associated with |nested_dispatcher_| which is used to determine
   // whether the |nested_dispatcher_| is allowed to receive events.
   aura::Window* associated_window_;
 
   DISALLOW_COPY_AND_ASSIGN(AcceleratorDispatcher);
 };
 
 }  // namespace ash
 
 #endif  // ASH_ACCELERATORS_ACCELERATOR_DISPATCHER_H_