Added back helper file accidentally deleted during test block 219 migration.

tests/lib_2/mirrors/enum_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.
 
 library test.enums;
 
 import 'dart:mirrors';
 import 'package:expect/expect.dart';
 import 'stringify.dart';
 
@@ skipping 45 matching lines @@
         'Variable(s(values) in s(Suite), static, final)',
         'Method(s(hashCode) in s(Suite), getter)',
         'Method(s(toString) in s(Suite))'
       ],
       reflectClass(Suite)
           .declarations
           .values
           .where((d) => !d.isPrivate)
           .map(stringify));
 }