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

tests/language_strong/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.
-
-foo() async* {
-  try {
-    int i = 0;
-    while (true) {
-      yield i++;
-    }
-  } finally {
-    throw "Error";
-  }
-}
-
-test() async {
-  var completer = new Completer();
-  var s;
-  s = foo().listen((e) async {
-    Expect.equals(0, e);
-    try {
-      await s.cancel();
-      Expect.fail("Did not throw");
-    } catch (e) {
-      Expect.equals("Error", e);
-      completer.complete();
-    }
-  });
-  await completer.future;
-}
-
-main() {
-  asyncStart();
-  test().then((_) => asyncEnd());
-}