Use callback_forward.h instead of callback.h where possible.

base/message_loop_proxy.h

 // Copyright (c) 2011 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_LOOP_PROXY_H_
 #define BASE_MESSAGE_LOOP_PROXY_H_
 #pragma once
 
 #include "base/base_export.h"
 #include "base/basictypes.h"
-#include "base/callback.h"
+#include "base/callback_forward.h"
 #include "base/memory/ref_counted.h"
 #include "base/task.h"
 
 namespace tracked_objects {
 class Location;
 } // namespace tracked_objects
 
 namespace base {
 
 struct MessageLoopProxyTraits;
@@ skipping 126 matching lines @@
 
 struct MessageLoopProxyTraits {
   static void Destruct(const MessageLoopProxy* proxy) {
     proxy->OnDestruct();
   }
 };
 
 }  // namespace base
 
 #endif  // BASE_MESSAGE_LOOP_PROXY_H_