Remove #pragma once from ash

ash/wm/user_activity_observer.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_WM_USER_ACTIVITY_OBSERVER_H_
 #define ASH_WM_USER_ACTIVITY_OBSERVER_H_
-#pragma once
 
 #include "ash/ash_export.h"
 #include "base/basictypes.h"
 
 namespace ash {
 
 // Interface for classes that want to be notified about user activity.
 // Implementations should register themselves with UserActivityDetector.
 class ASH_EXPORT UserActivityObserver {
  public:
   // Invoked periodically while the user is active (i.e. generating input
   // events).
   virtual void OnUserActivity() = 0;
 
  protected:
   UserActivityObserver() {}
   virtual ~UserActivityObserver() {}
 
   DISALLOW_COPY_AND_ASSIGN(UserActivityObserver);
 };
 
 }  // namespace ash
 
 #endif  // ASH_WM_USER_ACTIVITY_OBSERVER_H_