Add @MirrorsUsed annotations to speed up tests.

tests/lib/mirrors/closures_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 lib;
+
+@MirrorsUsed(targets: "lib")
 import 'dart:mirrors';
 import 'package:expect/expect.dart';
 import 'stringify.dart';
 
 testIntercepted() {
   var instance = [];
   var closureMirror = reflect(instance.toString);
   var methodMirror = closureMirror.function;
   Expect.equals(#toString, methodMirror.simpleName);
   Expect.equals('[]', closureMirror.apply([]).reflectee);
 }
 
 testNonIntercepted() {
   var closure = new Map().containsKey;
   var closureMirror = reflect(closure);
   var methodMirror = closureMirror.function;
   Expect.equals(#containsKey, methodMirror.simpleName);
   Expect.isFalse(closureMirror.apply([7]).reflectee);
 }
 
 main() {
   testIntercepted();
   testNonIntercepted();
 }