Don't make main async in the asyncstar_main_test file.

tests/language/yieldstar_pause_test.dart

 // Copyright (c) 2016, 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.
 
 import "dart:async";
 import "package:expect/expect.dart";
 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());
   var sub;
   sub = s.listen((v) {
     sub.pause();
     print(v);
     Timer.run(sub.resume);
   }, onDone: () {
     print("DONE");
     c.complete(null);
   });
 
-  await c.future;
-  asyncEnd();
+  c.future.whenComplete(asyncEnd);
 }
 
 Stream yieldStream(Stream s) async* {
   yield* s;
 }
 
 Stream mkStream() {
   var s = new StreamController(sync:true);
   // The close event has to be sent and received between
   // the pause and resume above.
   // Using a sync controller and a Timer.run(sub.resume) ensures this.
   Timer.run(() {
     s.add("event");
     s.close();
   });
   return s.stream;
 }