Don't make main async in the asyncstar_main_test file.

tests/language/yieldstar_pause_test.dart

Index: tests/language/yieldstar_pause_test.dart
diff --git a/tests/language/yieldstar_pause_test.dart b/tests/language/yieldstar_pause_test.dart
index fea834c261ea5a27fbc6d4de35357823d2d66341..945a0ee6c98c93de1f66736943f9990add506618 100644
--- a/tests/language/yieldstar_pause_test.dart
+++ b/tests/language/yieldstar_pause_test.dart
@@ -9,7 +9,7 @@ import "package:async_helper/async_helper.dart";
 // Regression test for http://dartbug.com/27205
 // If a yield-star completes while the stream is paused, it didn't resume.
 
-main() async {
+main() {
   asyncStart();
   var c = new Completer();
   var s = yieldStream(mkStream());
@@ -23,8 +23,7 @@ main() async {
     c.complete(null);
   });
 
-  await c.future;
-  asyncEnd();
+  c.future.whenComplete(asyncEnd);
 }
 
 Stream yieldStream(Stream s) async* {