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

base/message_pump_gtk.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_GTK_H_
 #define BASE_MESSAGE_PUMP_GTK_H_
-#pragma once
 
 #include "base/message_pump_glib.h"
 
 typedef union _GdkEvent GdkEvent;
 typedef struct _XDisplay Display;
 
 namespace base {
 
 // The documentation for this class is in message_pump_glib.h
 class MessagePumpObserver {
@@ skipping 50 matching lines @@
   static void EventDispatcher(GdkEvent* event, void* data);
 
   DISALLOW_COPY_AND_ASSIGN(MessagePumpGtk);
 };
 
 typedef MessagePumpGtk MessagePumpForUI;
 
 }  // namespace base
 
 #endif  // BASE_MESSAGE_PUMP_GTK_H_