Extract ClosedWorldRefiner implementation from ClosedWorldImpl to ClosedWorldBase

tests/compiler/dart2js/embedded_category_api_boundary_test.dart

 // Copyright (c) 2015, the Fletch 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.md file.
 
 /// Tests that analyzing everything from the libraries that are public from the
 /// embedded category does not cause elements from other libraries to be
 /// processed.
 library embedded_category_boundary_test;
 
 import 'package:expect/expect.dart';
@@ skipping 20 matching lines @@
 /// These elements are currently escaping from dart:async via
 /// `core._Resource#_readAsStream`.
 Set<String> whiteList = new Set.from([
   "function(StreamController#addError)",
   "getter(StreamController#stream)",
   "setter(StreamController#onListen)"
 ]);
 
 bool checkResults(Compiler compiler, CollectingDiagnosticHandler handler) {
   return compiler.enqueuer.resolution.processedEntities
-      .every((Element element) {
+      .every((MemberElement element) {
     if (whiteList.contains("$element")) return true;
     LibraryInfo info = libraries[element.library.canonicalUri.path];
     bool isAllowedInEmbedded =
         info.isInternal || info.categories.contains(Category.embedded);
     if (!isAllowedInEmbedded) {
       print(
           'Disallowed element: $element from ${element.library.canonicalUri}');
     }
     return isAllowedInEmbedded;
   });
 }