Migrated test block 168 to Dart 2.0.

tests/lib_2/async/future_delayed_error_test.dart

 // Copyright (c) 2012, 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_delayed_error_test;
 
 import 'package:async_helper/async_helper.dart';
 import "package:expect/expect.dart";
 import 'dart:async';
 
@@ skipping 17 matching lines @@
   completedFuture.catchError((error) {
     Expect.equals(error, "foobar");
     asyncEnd();
   });
 }
 
 main() {
   testImmediateError();
   testDelayedError();
 }