Migrate block 39 language/async_backwards ... /async_star_take.

tests/language_2/async_star_regression_23116_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.
 
 // Regression test for https://code.google.com/p/dart/issues/detail?id=23116
 
 import "package:expect/expect.dart";
 import "package:async_helper/async_helper.dart";
 import 'dart:async';
 
@@ skipping 13 matching lines @@
   // Ensure that execution of foo is not resumed - the future is not completed
   // yet.
   s.resume();
   completer2.complete(42);
 }
 
 main() {
   asyncStart();
   test().then((_) => asyncEnd());
 }