Make new StreamController be async by default.

tests/lib/async/stream_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_transform_test;
 
 import "package:expect/expect.dart";
 import 'dart:async';
 import '../../../pkg/unittest/lib/unittest.dart';
 import 'event_helper.dart';
 
 
 main() {
   // Regression tests for http://dartbug.com/8310 and 8311
 
   test("simpleDone", () {
-    StreamController c = new StreamController();
+    StreamController c = new StreamController(sync: true);
     Stream out = c.stream.handleError((x){}).handleError((x){});
     out.listen((v){}, onDone: expectAsync0(() {}));
     // Should not throw.
     c.close();
   });
 
   test("with events", () {
-    StreamController c = new StreamController();
+    StreamController c = new StreamController(sync: true);
     Events expected = new Events.fromIterable([10, 12]);
     Events input = new Events.fromIterable([1, 2, 3, 4, 5, 6, 7]);
     Events actual = new Events.capture(
         c.stream.map((x) => x * 2).where((x) => x > 5).skip(2).take(2));
     actual.onDone(expectAsync0(() {
       Expect.listEquals(expected.events, actual.events);
     }));
     input.replay(c);
   });
 
   test("paused events", () {
-    StreamController c = new StreamController();
+    StreamController c = new StreamController(sync: true);
     Events expected = new Events.fromIterable([10, 12]);
     Events input = new Events.fromIterable([1, 2, 3, 4, 5, 6, 7]);
     Events actual = new Events.capture(
         c.stream.map((x) => x * 2).where((x) => x > 5).skip(2).take(2));
     actual.onDone(expectAsync0(() {
       Expect.listEquals(expected.events, actual.events);
     }));
     actual.pause();
     input.replay(c);
     actual.resume();
   });
 
   test("closing after done", () {
-    var controller = new StreamController();
+    var controller = new StreamController(sync: true);
     controller.stream.map((e) => e).transform(new StreamTransformer(
         handleData: (element, sink) { sink.add(element); },
         handleDone: (sink) { sink.close(); })
     ).listen(expectAsync1((e) => expect(e, equals("foo"))));
 
     controller.add("foo");
     // Should not crash.
     controller.close();
   });
 }