Make new StreamController be async by default.

sdk/lib/io/io_sink.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;
 
 /**
  * Helper class to wrap a [StreamConsumer<List<int>>] and provide
  * utility functions for writing to the StreamConsumer directly. The
  * [IOSink] buffers the input given by all [StringSink] methods and will delay
@@ skipping 114 matching lines @@
   }
 
   StreamController<T> get _controller {
     if (_isBound) {
       throw new StateError("StreamSink is bound to a stream");
     }
     if (_isClosed) {
       throw new StateError("StreamSink is closed");
     }
     if (_controllerInstance == null) {
-      _controllerInstance = new StreamController<T>();
+      _controllerInstance = new StreamController<T>(sync: true);
       _controllerCompleter = new Completer();
       _target.addStream(_controller.stream)
           .then(
               (_) {
                 if (_isBound) {
                   // A new stream takes over - forward values to that stream.
                   _controllerCompleter.complete();
                   _controllerCompleter = null;
                   _controllerInstance = null;
                 } else {
@@ skipping 70 matching lines @@
 
   void writeln([Object obj = ""]) {
     write(obj);
     write("\n");
   }
 
   void writeCharCode(int charCode) {
     write(new String.fromCharCode(charCode));
   }
 }