Remove #pragma once from ash

ash/system/date/tray_date.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_SYSTEM_DATE_TRAY_DATE_H_
 #define ASH_SYSTEM_DATE_TRAY_DATE_H_
-#pragma once
 
 #include "ash/system/date/clock_observer.h"
 #include "ash/system/tray/system_tray_item.h"
 
 namespace views {
 class Label;
 }
 
 namespace ash {
 namespace internal {
@@ skipping 32 matching lines @@
 
   tray::TimeView* time_tray_;
 
   DISALLOW_COPY_AND_ASSIGN(TrayDate);
 };
 
 }  // namespace internal
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_DATE_TRAY_DATE_H_