Add @MirrorsUsed annotations to speed up tests.

tests/lib/mirrors/enum_test.dart

 // Copyright (c) 2015, 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.enums;
 
+@MirrorsUsed(targets: "test.enums")
 import 'dart:mirrors';
 import 'package:expect/expect.dart';
 import 'stringify.dart';
 
 class C {}
 enum Suite { CLUBS, DIAMONDS, SPADES, HEARTS }
 
 main() {
   Expect.isFalse(reflectClass(C).isEnum);
 
@@ skipping 27 matching lines @@
     'Variable(s(CLUBS) in s(Suite), static, final)',
     'Variable(s(DIAMONDS) in s(Suite), static, final)',
     'Variable(s(SPADES) in s(Suite), static, final)',
     'Variable(s(HEARTS) in s(Suite), static, final)',
     'Variable(s(values) in s(Suite), static, final)',
     'Method(s(hashCode) in s(Suite), getter)',
     'Method(s(toString) in s(Suite))'],
    reflectClass(Suite).declarations.values
        .where((d) => !d.isPrivate).map(stringify));
 }