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

tests/language/async_regression_23058_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 issue 23058.
-
-import "package:expect/expect.dart";
-import "package:async_helper/async_helper.dart";
-
-class A {
-  var x = new B();
-
-  foo() async {
-    return x.foo == 2 ? 42 : x.foo;
-  }
-}
-
-class B {
-  var x = 0;
-
-  get foo {
-    if (x == -1) {
-      return 0;
-    } else {
-      return x++;
-    }
-  }
-}
-
-main() {
-  asyncStart();
-  new A().foo().then((result) {
-    Expect.equals(1, result);
-    asyncEnd();
-  });
-}