Added back helper file accidentally deleted during test block 219 migration.

tests/lib_strong/mirrors/empty_test.dart

Index: tests/lib_strong/mirrors/empty_test.dart
diff --git a/tests/lib_strong/mirrors/empty_test.dart b/tests/lib_strong/mirrors/empty_test.dart
deleted file mode 100644
index 9e7763448321d05001303c7dd67a306a95381692..0000000000000000000000000000000000000000
--- a/tests/lib_strong/mirrors/empty_test.dart
+++ /dev/null
@@ -1,11 +0,0 @@
-// 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.
-
-import 'dart:mirrors';
-import 'empty.dart';
-
-main() {
-  var empty = currentMirrorSystem().findLibrary(#empty);
-  print(empty.location); // Used to crash VM.
-}