Add mirrors tests

test/codegen/lib/mirrors/empty_test.dart

 // Copyright (c) 2015, 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.
 
-// Test that `enum` is considered a keyword and therefore invalid as the name of
-// declarations.
+import 'dart:mirrors';
+import 'empty.dart';
 
 main() {
-  var enum; /// 01: compile-time error
+  var empty = currentMirrorSystem().findLibrary(#empty);
+  print(empty.location);  // Used to crash VM.
 }