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

base/message_pump_mac.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.
 
 // The basis for all native run loops on the Mac is the CFRunLoop.  It can be
 // used directly, it can be used as the driving force behind the similar
 // Foundation NSRunLoop, and it can be used to implement higher-level event
 // loops such as the NSApplication event loop.
 //
 // This file introduces a basic CFRunLoop-based implementation of the
@@ skipping 11 matching lines @@
 //
 // Typically, MessagePumpNSApplication only makes sense on a Cocoa
 // application's main thread.  If a CFRunLoop-based message pump is needed on
 // any other thread, one of the other concrete subclasses is preferrable.
 // MessagePumpMac::Create is defined, which returns a new NSApplication-based
 // or NSRunLoop-based MessagePump subclass depending on which thread it is
 // called on.
 
 #ifndef BASE_MESSAGE_PUMP_MAC_H_
 #define BASE_MESSAGE_PUMP_MAC_H_
-#pragma once
 
 #include "base/message_pump.h"
 
 #include <CoreFoundation/CoreFoundation.h>
 
 #if !defined(__OBJC__)
 class NSAutoreleasePool;
 #else  // !defined(__OBJC__)
 #import <AppKit/AppKit.h>
 
@@ skipping 249 matching lines @@
   // Requires NSApp to implement CrAppProtocol.
   BASE_EXPORT static bool IsHandlingSendEvent();
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(MessagePumpMac);
 };
 
 }  // namespace base
 
 #endif  // BASE_MESSAGE_PUMP_MAC_H_