Make ClosedWorld a `forTesting` property of ResolutionWorldBuilder.

pkg/compiler/lib/src/js_backend/enqueuer.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 dart2js.js.enqueue;
 
 import 'dart:collection' show Queue;
 
 import '../cache_strategy.dart' show CacheStrategy;
 import '../common/backend_api.dart' show Backend;
@@ skipping 68 matching lines @@
         newlySeenSelectors = cacheStrategy.newSet(),
         nativeEnqueuer = backend.nativeCodegenEnqueuer(),
         this._backend = backend,
         this.name = 'codegen enqueuer' {
     _impactVisitor = new EnqueuerImplImpactVisitor(this);
   }
 
   CodegenWorldBuilder get universe => _universe;
 
   // TODO(johnniwinther): Remove these hacks:
-  ClosedWorld get _world => _backend.compiler.closedWorld;
+  ClosedWorld get _world =>
+      _backend.compiler.resolverWorld.closedWorldForTesting;
   DumpInfoTask get _dumpInfoTask => _backend.compiler.dumpInfoTask;
 
   bool get queueIsEmpty => _queue.isEmpty;
 
   /// Returns [:true:] if this enqueuer is the resolution enqueuer.
   bool get isResolutionQueue => false;
 
   /**
    * Documentation wanted -- johnniwinther
    *
@@ skipping 395 matching lines @@
 
   @override
   Iterable<ClassEntity> get processedClasses => _processedClasses;
 }
 
 void removeFromSet(Map<String, Set<Element>> map, Element element) {
   Set<Element> set = map[element.name];
   if (set == null) return;
   set.remove(element);
 }