Add @MirrorsUsed annotations to speed up tests.

tests/lib/mirrors/instance_members_unimplemented_interface_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_unimplemented_interface;
 
+@MirrorsUsed(targets: "test.instance_members_unimplemented_interface")
 import 'dart:mirrors';
 import 'package:expect/expect.dart';
 
 class I {
   implementMe() {}
 }
 abstract class C implements I {}
 
 selectKeys(map, predicate) {
   return map.keys.where((key) => predicate(map[key]));
 }
 
 main() {
   ClassMirror cm = reflectClass(C);
 
   // N.B.: Does not include #implementMe.
   Expect.setEquals(
     [#hashCode,
      #runtimeType,
      #==,
      #noSuchMethod,
      #toString],
     selectKeys(cm.instanceMembers, (dm) => !dm.isPrivate));
   // Filter out private to avoid implementation-specific members of Object.
 }