Extract ClosedWorldRefiner implementation from ClosedWorldImpl to ClosedWorldBase

tests/compiler/dart2js/serialization/model_test_helper.dart

Index: tests/compiler/dart2js/serialization/model_test_helper.dart
diff --git a/tests/compiler/dart2js/serialization/model_test_helper.dart b/tests/compiler/dart2js/serialization/model_test_helper.dart
index b875a7345f19234621cb7c9783b1a5f7c2e7a441..53fec7c1a38246a42c0458ce221c0f492a09cf62 100644
--- a/tests/compiler/dart2js/serialization/model_test_helper.dart
+++ b/tests/compiler/dart2js/serialization/model_test_helper.dart
@@ -121,8 +121,9 @@ void checkResolutionEnqueuers(
     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;