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

tests/lib_2/mirrors/constructors_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.
 
 library test.constructors_test;
 
 import 'dart:mirrors';
 
 import 'package:expect/expect.dart';
 
@@ skipping 53 matching lines @@
       '[s()]', fooConstructors.values.map((m) => m.constructorName).toList());
   expect(
       '[s()]', barConstructors.values.map((m) => m.constructorName).toList());
   expect('[s(named)]',
       bazConstructors.values.map((m) => m.constructorName).toList());
   expect(
       '[s(), s(named)]',
       bizConstructors.values.map((m) => m.constructorName).toList()
         ..sort(compareSymbols));
 }