Make new StreamController be async by default.

sdk/lib/async/stream.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.async;
 
 // -------------------------------------------------------------------
 // Core Stream types
 // -------------------------------------------------------------------
 
@@ skipping 44 matching lines @@
 abstract class Stream<T> {
   Stream();
 
   /**
    * Creates a new single-subscription stream from the future.
    *
    * When the future completes, the stream will fire one event, either
    * data or error, and then close with a done-event.
    */
   factory Stream.fromFuture(Future<T> future) {
-    StreamController<T> controller = new StreamController<T>();
+    StreamController<T> controller = new StreamController<T>(sync: true);
     future.then((value) {
         controller.add(value);
         controller.close();
       },
       onError: (error) {
         controller.addError(error);
         controller.close();
       });
     return controller.stream;
   }
@@ skipping 31 matching lines @@
       controller.add(data);
     }
 
     void startPeriodicTimer() {
       assert(timer == null);
       timer = new Timer.periodic(period, (Timer timer) {
         sendEvent();
       });
     }
 
-    controller = new StreamController<T>(
+    controller = new StreamController<T>(sync: true,
         onListen: () {
           watch.start();
           startPeriodicTimer();
         },
         onPause: () {
           timer.cancel();
           timer = null;
           watch.stop();
         },
         onResume: () {
@@ skipping 1113 matching lines @@
    *
    * If a [moveNext] call has been made, it will complete with `false` as value,
    * as will all further calls to [moveNext].
    *
    * If you need to stop listening for values before the stream iterator is
    * automatically closed, you must call [cancel] to ensure that the stream
    * is properly closed.
    */
   void cancel();
 }