Make sure we always unsubscribe from a stream, in http-impl.

sdk/lib/io/http_impl.dart

 // Copyright (c) 2013, 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.
 
 part of dart.io;
 
 class _HttpIncoming extends Stream<List<int>> {
   final int _transferLength;
   final Completer _dataCompleter = new Completer();
   Stream<List<int>> _stream;
@@ skipping 549 matching lines @@
   }
 
   _ensureController() {
     if (_controller != null) return;
     _controller = new StreamController(onPause: _onPause,
                                        onResume: _onPause,
                                        onListen: _onListen,
                                        onCancel: _onListen);
     _outbound._addStream(_controller.stream)
         .then((_) {
+                _onListen();  // Make sure we unsubscribe.
                 _done();
                 _closeCompleter.complete(_outbound);
               },
               onError: (error) {
                 if (!_done(error)) {
                   _closeCompleter.completeError(error);
                 }
               });
   }
 
@@ skipping 1650 matching lines @@
 
 
 class _RedirectInfo implements RedirectInfo {
   const _RedirectInfo(int this.statusCode,
                       String this.method,
                       Uri this.location);
   final int statusCode;
   final String method;
   final Uri location;
 }