Fix problem that caused anonymous mixin applications to be named "null".

dart/tests/lib/mirrors/mixin_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.
 
 // TODO(ahe): This test is sligthly broken but provides temporary test coverage
 // for dart2js. See http://dartbug.com/12464.
 
 library test.mixin_test;
 
-@MirrorsUsed(targets: 'test.mixin_test, test.model, Object', override: '*')
 import 'dart:mirrors';
 
 import 'package:expect/expect.dart';
 
 import 'model.dart';
 import 'stringify.dart';
 
 class Mixin {
   int i;
   m() {}
@@ skipping 276 matching lines @@
   testMixin();
   testMixin2();
   testMixinApplication();
   testMixinApplicationA();
   testUnusedMixinApplication();
   testSubclass();
   testSubclass2();
   testSubclassA();
   testSubclass2A();
 }