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

tests/language/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';
-
-Stream<int> foo(Completer completer, Future future) async* {
-  completer.complete(100);
-  int x = await future;
-  Expect.equals(42, x);
-}
-
-test() async {
-  Completer completer1 = new Completer();
-  Completer completer2 = new Completer();
-  StreamSubscription s = foo(completer1, completer2.future).listen((v) => null);
-  await completer1.future;
-  // At this moment foo is waiting on the given future.
-  s.pause();
-  // Ensure that execution of foo is not resumed - the future is not completed
-  // yet.
-  s.resume();
-  completer2.complete(42);
-}
-
-main() {
-  asyncStart();
-  test().then((_) => asyncEnd());
-}