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

tests/language_2/async_star_cancel_and_throw_in_finally_test.dart

 // Copyright (c) 2015, 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";
 
 // When an exception is thrown in the finally block cleaning up after a cancel,
 // the future returned from cancel should complete with an error.
@@ skipping 22 matching lines @@
       completer.complete();
     }
   });
   await completer.future;
 }
 
 main() {
   asyncStart();
   test().then((_) => asyncEnd());
 }