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

tests/standalone/io/http_server_early_client_close2_test.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.
+//
+// VMOptions=
+// VMOptions=--short_socket_read
+// VMOptions=--short_socket_write
+// VMOptions=--short_socket_read --short_socket_write
 
 import "package:expect/expect.dart";
 import "dart:async";
 import "dart:io";
 import "dart:isolate";
 
 main() {
   HttpServer.bind("127.0.0.1", 0).then((server) {
     server.listen(
       (request) {
@@ skipping 14 matching lines @@
             makeRequest();
           } else {
             server.close();
           }
         });
       });
     }
     makeRequest();
   });
 }