Get rid of the polyfill identity set implementation in favour of a

pkg/serialization/lib/serialization.dart

 // Copyright (c) 2012, 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.
 
 /**
  * This provides a general-purpose serialization facility for Dart objects. A
  * [Serialization] is defined in terms of [SerializationRule]s and supports
  * reading and writing to different formats.
  *
  * Setup
@@ skipping 130 matching lines @@
  * or as an additional parameter to the reading methods.
  *
  *     new Serialization()
  *       ..addRuleFor(new Person(), constructorFields: ["name"])
  *       ..externalObjects['Person'] = reflect(new Person()).type;
  */
 library serialization;
 
 import 'src/mirrors_helpers.dart';
 import 'src/serialization_helpers.dart';
-import 'src/polyfill_identity_set.dart';
 import 'dart:json' show JSON;
 
 part 'src/reader_writer.dart';
 part 'src/serialization_rule.dart';
 part 'src/basic_rule.dart';
 
 /**
  * This class defines a particular serialization scheme, in terms of
  * [SerializationRule] instances, and supports reading and writing them.
  * See library comment for examples of usage.
@@ skipping 214 matching lines @@
     // and get their types. If only we had class literals implemented...
     var closureRule = new ClosureToMapRule.stub([].runtimeType);
     var basicRule = new BasicRule(reflect(null).type, '', [], [], []);
 
     var meta = new Serialization()
       ..selfDescribing = false
       ..addRuleFor(new ListRule())
       ..addRuleFor(new PrimitiveRule())
       ..addRuleFor(new ListRuleEssential())
       ..addRuleFor(basicRule,
-          constructorFields: ['typeWrapped',
+          constructorFields: ['type',
             'constructorName',
             'constructorFields', 'regularFields', []],
           fields: [])
       ..addRule(new ClassMirrorRule());
     meta.externalObjects = externalObjects;
     return meta;
   }
 }
 
 /**
  * An exception class for errors during serialization.
  */
 class SerializationException implements Exception {
   final String message;
   const SerializationException([this.message]);
 }