Migrating a block of dart 1 tests to dart 2

tests/language_2/class_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.
 
 import "package:expect/expect.dart";
 
 // Tests basic classes and methods.
 class ClassTest {
   ClassTest() {}
 
@@ skipping 157 matching lines @@
   }
 
   Sub() : super(42) {
     y_ = 0;
   }
 }
 
 main() {
   ClassTest.testMain();
 }