Migrate language/async_backwards... ... language/async_star_take...

tests/language_2/async_star_no_cancel2_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";
 
 var events = [];
 
@@ skipping 39 matching lines @@
       asyncEnd();
     });
 
     events.add("invoke cancel");
     await subscription.cancel();
     // This line should never be reached, since the cancel-future doesn't
     // complete.
     cancelFinished = true;
   });
 }