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

base/message_pump_libevent.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_LIBEVENT_H_
 #define BASE_MESSAGE_PUMP_LIBEVENT_H_
-#pragma once
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/memory/weak_ptr.h"
 #include "base/message_pump.h"
 #include "base/observer_list.h"
 #include "base/threading/thread_checker.h"
 #include "base/time.h"
 
 // Declare structs we need from libevent.h rather than including it
@@ skipping 155 matching lines @@
   event* wakeup_event_;
 
   ObserverList<IOObserver> io_observers_;
   ThreadChecker watch_file_descriptor_caller_checker_;
   DISALLOW_COPY_AND_ASSIGN(MessagePumpLibevent);
 };
 
 }  // namespace base
 
 #endif  // BASE_MESSAGE_PUMP_LIBEVENT_H_