Migrated test block 168 to Dart 2.0.

tests/lib_2/async/future_foreach_test.dart

 // Copyright (c) 2017, 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.
 
 library future_foreach_test;
 
 import 'package:async_helper/async_helper.dart';
 import "package:expect/expect.dart";
 import 'dart:async';
 
@@ skipping 91 matching lines @@
           return new Future.microtask(() {});
       }
     }).then((_) {
       Expect.fail("Did not throw");
     }, onError: (e) {
       Expect.equals("ERROR", e);
       asyncEnd();
     });
   }
 }