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

net/base/completion_callback.h

Index: net/base/completion_callback.h
diff --git a/net/base/completion_callback.h b/net/base/completion_callback.h
index 7474793acbdc77134433e150918a980b75ad2ca3..cea6be36cb980ff2631fbac7acda8593068f3bb6 100644
--- a/net/base/completion_callback.h
+++ b/net/base/completion_callback.h
@@ -8,6 +8,7 @@
 
 #include "base/callback_old.h"
 #include "base/callback.h"
+#include "base/cancelable_callback.h"
 
 namespace net {
 
@@ -27,6 +28,8 @@ class OldCompletionCallbackImpl :
   }
 };
 
+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