Migrated test block 167 to Dart 2.0.

tests/lib_2/async/catch_errors21_test.dart

 // Copyright (c) 2013, 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 'package:async_helper/async_helper.dart';
 import "package:expect/expect.dart";
 import 'dart:async';
 import 'catch_errors.dart';
 
 main() {
@@ skipping 35 matching lines @@
         "caught: 3",
         "caught: 4",
       ], events);
       asyncEnd();
     });
   });
 
   [1, 2, 3, 4].forEach(controller.add);
   controller.close();
 }