Add mirrors tests

test/codegen/lib/mirrors/library_metatarget_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.
+
+// Regression test for the combined use of metatargets and library tags.
+
+library topLib;
+
+import 'library_metatarget_test_lib.dart';
+import 'library_metatarget_test_annotations_lib.dart';
+
+@MirrorsUsed(metaTargets:const [Reflectable])
+import 'dart:mirrors';
+
+void main() {
+  print(new A());
+}