Make new StreamController be async by default.

tests/lib/async/stream_event_transform_test.dart

 // Copyright (c) 2011, 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.
 
 library stream_event_transform_test;
 
 import "package:expect/expect.dart";
 import 'dart:async';
 import '../../../pkg/unittest/lib/unittest.dart';
 import 'event_helper.dart';
@@ skipping 28 matching lines @@
   }
 
   void handleDone(EventSink<int> sink) {
     sink.add(99);
     sink.close();
   }
 }
 
 main() {
   {
-    StreamController c = new StreamController();
+    StreamController c = new StreamController(sync: true);
     Events expected = new Events()..error("0")..add(1)
                                   ..error("1")..add(2)
                                   ..add(3)..error("4")
                                   ..add(99)..close();
     Events input = new Events()..add(0)..add(1)..error("3")..close();
     Events actual = new Events.capture(
         c.stream.transform(new EventTransformer()));
     actual.onDone(() {
       Expect.listEquals(expected.events, actual.events);
     });
     input.replay(c);
   }
 
   {
-    StreamController c = new StreamController();
+    StreamController c = new StreamController(sync: true);
     Events expected = new Events()..error("0")..add(1)
                                   ..error("1")..add(2)
                                   ..add(3)..error("4")
                                   ..add(99)..close();
     Events input = new Events()..add(0)..add(1)..error("3")..close();
     Events actual = new Events.capture(
         c.stream.transform(new StreamTransformer(
             handleData: handleData,
             handleError: handleError,
             handleDone: handleDone
         )));
     actual.onDone(() {
       Expect.listEquals(expected.events, actual.events);
     });
     input.replay(c);
   }
 }