Make new StreamController be async by default.

tests/lib/async/stream_single_test.dart

Index: tests/lib/async/stream_single_test.dart
diff --git a/tests/lib/async/stream_single_test.dart b/tests/lib/async/stream_single_test.dart
index fe0b384fee2068c4d6b1440b105ee43f48436bd4..4c3c486d76c0dc79c9963b5ff58c517dc491b029 100644
--- a/tests/lib/async/stream_single_test.dart
+++ b/tests/lib/async/stream_single_test.dart
@@ -13,21 +13,21 @@ import 'event_helper.dart';
 
 main() {
   test("single", () {
-    StreamController c = new StreamController();
+    StreamController c = new StreamController(sync: true);
     Future f = c.stream.single;
     f.then(expectAsync1((v) { Expect.equals(42, v);}));
     new Events.fromIterable([42]).replay(c);
   });
 
   test("single empty", () {
-    StreamController c = new StreamController();
+    StreamController c = new StreamController(sync: true);
     Future f = c.stream.single;
     f.catchError(expectAsync1((error) { Expect.isTrue(error is StateError); }));
     new Events.fromIterable([]).replay(c);
   });
 
   test("single error", () {
-    StreamController c = new StreamController();
+    StreamController c = new StreamController(sync: true);
     Future f = c.stream.single;
     f.catchError(expectAsync1((error) { Expect.equals("error", error); }));
     Events errorEvents = new Events()..error("error")..close();
@@ -35,7 +35,7 @@ main() {
   });
 
   test("single error 2", () {
-    StreamController c = new StreamController();
+    StreamController c = new StreamController(sync: true);
     Future f = c.stream.single;
     f.catchError(expectAsync1((error) { Expect.equals("error", error); }));
     Events errorEvents = new Events()..error("error")..error("error2")..close();
@@ -43,7 +43,7 @@ main() {
   });
 
   test("single error 3", () {
-    StreamController c = new StreamController();
+    StreamController c = new StreamController(sync: true);
     Future f = c.stream.single;
     f.catchError(expectAsync1((error) { Expect.equals("error", error); }));
     Events errorEvents = new Events()..add(499)..error("error")..close();