Extract ClosedWorldRefiner implementation from ClosedWorldImpl to ClosedWorldBase

tests/compiler/dart2js/serialization/model_test_helper.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 dart2js.serialization_model_test;
 
 import 'dart:async';
 import 'dart:io';
 import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
@@ skipping 103 matching lines @@
 void checkResolutionEnqueuers(
     BackendUsage backendUsage1,
     BackendUsage backendUsage2,
     ResolutionEnqueuer enqueuer1,
     ResolutionEnqueuer enqueuer2,
     {bool typeEquivalence(ResolutionDartType a, ResolutionDartType b):
         areTypesEquivalent,
     bool elementFilter(Element element),
     bool verbose: false}) {
   checkSets(enqueuer1.processedEntities, enqueuer2.processedEntities,
-      "Processed element mismatch", areElementsEquivalent,
-      elementFilter: elementFilter, verbose: verbose);
+      "Processed element mismatch", areElementsEquivalent, elementFilter: (e) {
+    return elementFilter != null ? elementFilter(e) : true;
+  }, verbose: verbose);
 
   ElementResolutionWorldBuilder worldBuilder1 = enqueuer1.worldBuilder;
   ElementResolutionWorldBuilder worldBuilder2 = enqueuer2.worldBuilder;
 
   checkMaps(
       worldBuilder1.getInstantiationMap(),
       worldBuilder2.getInstantiationMap(),
       "Instantiated classes mismatch",
       areElementsEquivalent,
       (a, b) => areInstantiationInfosEquivalent(a, b, typeEquivalence),
@@ skipping 318 matching lines @@
 }
 
 bool areInstancesEquivalent(Instance instance1, Instance instance2,
     bool typeEquivalence(ResolutionDartType a, ResolutionDartType b)) {
   ResolutionInterfaceType type1 = instance1.type;
   ResolutionInterfaceType type2 = instance2.type;
   return typeEquivalence(type1, type2) &&
       instance1.kind == instance2.kind &&
       instance1.isRedirection == instance2.isRedirection;
 }