Unregister callbacks from socket, when we return the socket for reuse.

runtime/bin/http_impl.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 class _HttpHeaders implements HttpHeaders {
   _HttpHeaders() : _headers = new Map<String, List<String>>();
 
   List<String> operator[](String name) {
     name = name.toLowerCase();
     return _headers[name];
@@ skipping 1329 matching lines @@
       if (socketConnections.isEmpty()) {
         _evictionTimer.cancel();
         _evictionTimer = null;
       }
     }
 
     return connection;
   }
 
   void _returnSocketConnection(_SocketConnection socketConn) {
+    // Mark socket as returned to unregister from the old connection.
+    socketConn._markReturned();
+
     // If the HTTP client is beeing shutdown don't return the connection.
     if (_shutdown) {
       socketConn._socket.close();
       return;
     };
 
     String key = _connectionKey(socketConn._host, socketConn._port);
 
     // Get or create the connection list for this key.
     Queue sockets = _openSockets[key];
@@ skipping 21 matching lines @@
                 }
               }
             });
       }
       _evictionTimer = new Timer.repeating(10000, _handleEviction);
     }
 
     // Return connection.
     _activeSockets.remove(socketConn);
     sockets.addFirst(socketConn);
-    socketConn._markReturned();
   }
 
   Function _onOpen;
   Map<String, Queue<_SocketConnection>> _openSockets;
   Set<_SocketConnection> _activeSockets;
   Timer _evictionTimer;
   bool _shutdown;  // Has this HTTP client been shutdown?
 }