Add @MirrorsUsed annotations to speed up tests.

tests/lib/mirrors/instance_members_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 test.instance_members;
 
+@MirrorsUsed(targets: "test.instance_members")
 import 'dart:mirrors';
 import 'package:expect/expect.dart';
 
 import 'declarations_model.dart' as declarations_model;
 
 selectKeys(map, predicate) {
   return map.keys.where((key) => predicate(map[key]));
 }
 
 main() {
@@ skipping 28 matching lines @@
 
   Expect.setEquals(
     [#instanceVariable,
      const Symbol('instanceVariable='),
      #inheritedInstanceVariable,
      const Symbol('inheritedInstanceVariable='),
      #mixinInstanceVariable,
      const Symbol('mixinInstanceVariable=')],
     selectKeys(cm.instanceMembers, (dm) => !dm.isPrivate && dm.isSynthetic));
 }