Add mirrors tests

test/codegen/lib/mirrors/null2_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.null_test;
+
+import 'dart:mirrors';
+
 import 'package:expect/expect.dart';
 
-class A {
-  toString() {
-    if (false
-          || true  /// 01: runtime error
-        ) {
-      return 499;
-    } else {
-      return "ok";
-    }
+main() {
+  InstanceMirror nullMirror = reflect(null);
+  for (int i = 0; i < 10; i++) {
+    Expect.isTrue(nullMirror.getField(#hashCode).reflectee is int);
   }
 }
-
-main() {
-  print(new A());
-}