Add mirrors tests

test/codegen/lib/mirrors/native_class_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.native_class_test;
+
+import 'dart:html';
+
+@MirrorsUsed(targets: 'dart.dom.html.Element')
+import 'dart:mirrors';
+
+import 'stringify.dart';
+
+main() {
+  expect('s(dart.dom.html.Element)', reflectClass(Element).qualifiedName);
+  expect(
+      's(dart.dom.html.Node)', reflectClass(Element).superclass.qualifiedName);
+  window.postMessage('unittest-suite-success', '*');
+}