Make new StreamController be async by default.

sdk/lib/io/mime_multipart_parser.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.
 
 part of dart.io;
 
 
 /**
  * A Mime Multipart class representing each part parsed by
  * [MimeMultipartTransformer]. The data is streamed in as it become available.
@@ skipping 83 matching lines @@
   void _resumeStream() {
     _subscription.resume();
   }
 
   void _pauseStream() {
     _subscription.pause();
   }
 
   Stream<MimeMultipart> bind(Stream<List<int>> stream) {
     _controller = new StreamController(
+        sync: true,
         onPause: _pauseStream,
         onResume:_resumeStream,
         onCancel: () {
           _subscription.cancel();
         },
         onListen: () {
           _subscription = stream.listen(
               (data) {
                 assert(_buffer == null);
                 _pauseStream();
@@ skipping 172 matching lines @@
               // Start of new header field.
               _headerField.writeCharCode(_toLowerCase(byte));
               _state = _HEADER_FIELD;
             }
           }
           break;
 
         case _HEADER_ENDING:
           _expect(byte, _CharCode.LF);
           _multipartController = new StreamController(
+              sync: true,
               onPause: () {
                 _pauseStream();
               },
               onResume: () {
                 _resumeStream();
                 _parse();
               });
           _controller.add(
               new _MimeMultipart(_headers, _multipartController.stream));
           _headers = null;
@@ skipping 88 matching lines @@
     }
   }
 }
 
 
 class MimeMultipartException implements Exception {
   const MimeMultipartException([String this.message = ""]);
   String toString() => "MimeMultipartException: $message";
   final String message;
 }