Remove #pragma once. Just from base/ for now.

base/message_pump_win.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 BASE_MESSAGE_PUMP_WIN_H_
 #define BASE_MESSAGE_PUMP_WIN_H_
-#pragma once
 
 #include <windows.h>
 
 #include <list>
 
 #include "base/base_export.h"
 #include "base/basictypes.h"
 #include "base/message_pump.h"
 #include "base/message_pump_dispatcher.h"
 #include "base/message_pump_observer.h"
@@ skipping 314 matching lines @@
   // This list will be empty almost always. It stores IO completions that have
   // not been delivered yet because somebody was doing cleanup.
   std::list<IOItem> completed_io_;
 
   ObserverList<IOObserver> io_observers_;
 };
 
 }  // namespace base
 
 #endif  // BASE_MESSAGE_PUMP_WIN_H_