iwyu: Use callback_old.h where appropriate, part 1.

net/base/completion_callback.h

 // Copyright (c) 2006-2008 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 NET_BASE_COMPLETION_CALLBACK_H__
 #define NET_BASE_COMPLETION_CALLBACK_H__
 #pragma once
 
-#include "base/callback.h"
+#include "base/callback_old.h"
 
 namespace net {
 
 // A callback specialization that takes a single int parameter.  Usually this
 // is used to report a byte count or network error code.
 typedef Callback1<int>::Type CompletionCallback;
 
 // Used to implement a CompletionCallback.
 template <class T>
 class CompletionCallbackImpl :
@@ skipping 31 matching lines @@
     }
   }
 
  private:
   bool is_canceled_;
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_COMPLETION_CALLBACK_H__