Add @MirrorsUsed annotations to speed up tests.

tests/lib/mirrors/raw_type_test.dart

Index: tests/lib/mirrors/raw_type_test.dart
diff --git a/tests/lib/mirrors/raw_type_test.dart b/tests/lib/mirrors/raw_type_test.dart
index d57e48660e5a9970a5a3370b5b50d0b40fc17419..e62696d57b96db78e1e6178c319063537e70da2b 100644
--- a/tests/lib/mirrors/raw_type_test.dart
+++ b/tests/lib/mirrors/raw_type_test.dart
@@ -2,6 +2,9 @@
 // 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 lib;
+
+@MirrorsUsed(targets: "lib")
 import 'dart:mirrors';
 
 import 'package:expect/expect.dart';