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

pkg/serialization/test/serialization_test.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.
 
 library serialization_test;
 
 import '../../unittest/lib/unittest.dart';
 import '../lib/serialization.dart';
 import '../lib/src/serialization_helpers.dart';
 import '../lib/src/mirrors_helpers.dart';
@@ skipping 297 matching lines @@
   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())
     // TODO(alanknight): Handle the ClosureToMapRule as well.
     // Note that we're passing in a constant for one of the fields.
     ..addRuleFor(basicRule,
-        constructorFields: ['typeWrapped',
+        constructorFields: ['type',
           'constructorName',
           'constructorFields', 'regularFields', []],
         fields: [])
      ..addRuleFor(new Serialization()).specialTreatmentFor('rules',
          (InstanceMirror s, List rules) {
              rules.forEach((x) => s.reflectee.addRule(x));
          })
     ..addRule(new ClassMirrorRule());
   return meta;
 }
@@ skipping 124 matching lines @@
   expect(m2.parent, m1);
   expect(m3.parent, m1);
   expect(m1.parent, isNull);
 }
 
 /** Extract the state from [object] using the rules in [s] and return it. */
 states(Object object, Serialization s) {
   var rules = s.rulesFor(object);
   return rules.map((x) => x.extractState(object, doNothing));
 }