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

tests/language_2/async_star_take_reyield_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";
 
 expectList(stream, list) {
   return stream.toList().then((v) {
     Expect.listEquals(v, list);
   });
 }
 
 Stream makeStream(int n) async* {
   for (int i = 0; i < n; i++) yield i;
 }
 
 main() {
   fivePartialSums(Stream s) async* {
     var r = 0;
     await for (var v in s.take(5)) yield r += v;
   }
 
   asyncStart();
   expectList(fivePartialSums(makeStream(10)), [0, 1, 3, 6, 10])
       .then(asyncSuccess);
 }