Change reflective serialization rules to be able to take type literals

pkg/serialization/test/no_library_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.
 
 import 'package:serialization/serialization.dart';
 import 'package:unittest/unittest.dart';
 
 class Thing {
   var name;
 }
 
 void main() {
 
   test("Serializing something without a library directive", () {
     var thing = new Thing()..name = 'testThing';
     var s = new Serialization()
-      ..addRuleFor(thing);
+      ..addRuleFor(Thing);
     var serialized = s.write(thing);
     var newThing = s.read(serialized);
     expect(thing.name, newThing.name);
   });
 }