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

base/message_pump_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 BASE_MESSAGE_PUMP_OBSERVER_H
 #define BASE_MESSAGE_PUMP_OBSERVER_H
-#pragma once
 
 #include "base/event_types.h"
 
 namespace base {
 
 enum EventStatus {
   EVENT_CONTINUE,    // The event should be dispatched as normal.
 #if defined(USE_X11)
   EVENT_HANDLED      // The event should not be processed any farther.
 #endif
@@ skipping 20 matching lines @@
   // will not be called if WillProcessEvent returns EVENT_HANDLED.
   virtual void DidProcessEvent(const NativeEvent& event) = 0;
 
  protected:
   virtual ~MessagePumpObserver() {}
 };
 
 }  // namespace base
 
 #endif  // BASE_MESSAGE_PUMP_OBSERVER_VIEWS_H