Migrating a block of dart 1 tests to dart 2

tests/language_2/class_syntax2_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.
 
 // Regression test for dart2js bug http://dartbug.com/11570.
 
 import 'package:expect/expect.dart';
 
 void main() {
   var c = new Cool(true);
   Expect.stringEquals('{}', '${c.thing}');
 
   c = new Cool(false);
   Expect.stringEquals('[]', '${c.thing}');
 
   c = new Cool.alt(true);
   Expect.stringEquals('{}', '${c.thing}');
 
   c = new Cool.alt(false);
   Expect.stringEquals('[]', '${c.thing}');
 }
 
 class Cool {
   final thing;
 
   Cool(bool option) : thing = option ? <String, String>{} : <String>[];
   Cool.alt(bool option) : thing = !option ? <String>[] : <String, String>{};
 }