Separates out accelerator handling in windowmanager

ash/mus/window_manager_observer.h

 // Copyright 2016 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_MUS_WINDOW_OBSERVER_H_
 #define ASH_MUS_WINDOW_OBSERVER_H_
 
-#include <stdint.h>
-
-namespace ui {
-class Event;
-}
-
 namespace ash {
 namespace mus {
 
 class RootWindowController;
 
 class WindowManagerObserver {
  public:
   // Called when the WindowTreeClient associated with the WindowManager is
   // about to be destroyed.
   virtual void OnWindowTreeClientDestroyed() {}
 
-  virtual void OnAccelerator(uint32_t id, const ui::Event& event) {}
-
   virtual void OnRootWindowControllerAdded(RootWindowController* controller) {}
   virtual void OnWillDestroyRootWindowController(
       RootWindowController* controller) {}
 
  protected:
   virtual ~WindowManagerObserver() {}
 };
 
 }  // namespace mus
 }  // namespace ash
 
 #endif  // ASH_MUS_WINDOW_OBSERVER_H_