Add mirrors tests

test/codegen/lib/mirrors/superclass_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.superclass;
+
+import 'dart:mirrors';
+import 'package:expect/expect.dart';
+
+class MyClass {
+}
+
+main() {
+  var cls = reflectClass(MyClass);
+  Expect.isNotNull(cls, 'Failed to reflect on MyClass.');
+  var superclass = cls.superclass;
+  Expect.isNotNull(superclass, 'Failed to obtain superclass of MyClass.');
+  Expect.equals(
+      reflectClass(Object), superclass, 'Superclass of MyClass is not Object.');
+  Expect.isNull(superclass.superclass, 'Superclass of Object is not null.');
+}