Remove BindStateHolder and have Bind() return a Callback<> object directly.

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 cea6be36cb980ff2631fbac7acda8593068f3bb6..204299422fc447b3e50b444d25d4480a56fb3a7b 100644
--- a/net/base/completion_callback.h
+++ b/net/base/completion_callback.h
@@ -60,6 +60,13 @@ class CancelableOldCompletionCallback :
   bool is_canceled_;
 };
 
+// Helper function for using OldCompletionCallback objects with
+// the newer CompletionCallback APIs.
+//
+// This is a transitional function and should be removed when
+// OldCompletionCallbackAdapter is deleted.
+void OldCompletionCallbackAdapter(OldCompletionCallback* old_callback, int rv);
+
 }  // namespace net
 
 #endif  // NET_BASE_COMPLETION_CALLBACK_H__