base::Bind: Implement a 1-arity CancelableCallback and use this to implement

net/base/completion_callback.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 NET_BASE_COMPLETION_CALLBACK_H__
 #define NET_BASE_COMPLETION_CALLBACK_H__
 #pragma once
 
 #include "base/callback_old.h"
 #include "base/callback.h"
+#include "base/cancelable_callback.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 OldCompletionCallback;
 typedef base::Callback<void(int)> CompletionCallback;
 
 // Used to implement a OldCompletionCallback.
 template <class T>
 class OldCompletionCallbackImpl :
     public CallbackImpl< T, void (T::*)(int), Tuple1<int> > {
  public:
   OldCompletionCallbackImpl(T* obj, void (T::* meth)(int))
     : CallbackImpl< T, void (T::*)(int),
                     Tuple1<int> >::CallbackImpl(obj, meth) {
   }
 };
 
+typedef base::CancelableCallback<void(int)> CancelableCompletionCallback;
+
 // CancelableOldCompletionCallback is used for completion callbacks
 // which may outlive the target for the method dispatch. In such a case, the
 // provider of the callback calls Cancel() to mark the callback as
 // "canceled". When the canceled callback is eventually run it does nothing
 // other than to decrement the refcount to 0 and free the memory.
 template <class T>
 class CancelableOldCompletionCallback :
     public OldCompletionCallbackImpl<T>,
     public base::RefCounted<CancelableOldCompletionCallback<T> > {
  public:
@@ skipping 13 matching lines @@
     }
   }
 
  private:
   bool is_canceled_;
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_COMPLETION_CALLBACK_H__