Make new StreamController be async by default.

tests/standalone/io/io_sink_test.dart

Index: tests/standalone/io/io_sink_test.dart
diff --git a/tests/standalone/io/io_sink_test.dart b/tests/standalone/io/io_sink_test.dart
index 1c964486f7d515f3588c064e98595f094e6b8753..de830442e394cb7a0494d9df4e47933af4d04913 100644
--- a/tests/standalone/io/io_sink_test.dart
+++ b/tests/standalone/io/io_sink_test.dart
@@ -65,7 +65,7 @@ void testAddClose() {
 void testAddStreamClose() {
   {
     var sink = new IOSink(new TestConsumer([0]));
-    var controller = new StreamController();
+    var controller = new StreamController(sync: true);
     sink.addStream(controller.stream)
         .then((_) {
           sink.close();
@@ -75,7 +75,7 @@ void testAddStreamClose() {
   }
   {
     var sink = new IOSink(new TestConsumer([0, 1, 2]));
-    var controller = new StreamController();
+    var controller = new StreamController(sync: true);
     sink.addStream(controller.stream)
         .then((_) {
           sink.close();
@@ -90,7 +90,7 @@ void testAddStreamClose() {
 void testAddStreamAddClose() {
   {
     var sink = new IOSink(new TestConsumer([0, 1]));
-    var controller = new StreamController();
+    var controller = new StreamController(sync: true);
     sink.addStream(controller.stream)
         .then((_) {
           sink.add([1]);