Move closed world reasoning methods from ClassWorld to ClosedWorld.

pkg/compiler/lib/src/js_backend/backend.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 js_backend.backend;
 
 import 'dart:async' show Future;
 
 import 'package:js_runtime/shared/embedded_names.dart' as embeddedNames;
 
@@ skipping 40 matching lines @@
 import '../universe/world_impact.dart'
     show
         ImpactStrategy,
         ImpactUseCase,
         TransformedWorldImpact,
         WorldImpact,
         WorldImpactBuilder,
         WorldImpactVisitor,
         StagedWorldImpactBuilder;
 import '../util/util.dart';
-import '../world.dart' show ClassWorld;
+import '../world.dart' show ClosedWorld;
 import 'backend_helpers.dart';
 import 'backend_impact.dart';
 import 'backend_serialization.dart' show JavaScriptBackendSerialization;
 import 'checked_mode_helpers.dart';
 import 'constant_handler_javascript.dart';
 import 'custom_elements_analysis.dart';
 import 'enqueuer.dart';
 import 'js_interop_analysis.dart' show JsInteropAnalysis;
 import 'kernel_task.dart';
 import 'lookup_map_analysis.dart' show LookupMapAnalysis;
@@ skipping 904 matching lines @@
           Set<ClassElement> nativeSubclasses =
               nativeSubclassesOfMixin(classElement);
           if (nativeSubclasses != null) result.addAll(nativeSubclasses);
         }
       }
       return result;
     });
   }
 
   Set<ClassElement> nativeSubclassesOfMixin(ClassElement mixin) {
-    ClassWorld classWorld = compiler.closedWorld;
-    Iterable<MixinApplicationElement> uses = classWorld.mixinUsesOf(mixin);
+    ClosedWorld closedWorld = compiler.closedWorld;
+    Iterable<MixinApplicationElement> uses = closedWorld.mixinUsesOf(mixin);
     Set<ClassElement> result = null;
     for (MixinApplicationElement use in uses) {
-      classWorld.forEachStrictSubclassOf(use, (ClassElement subclass) {
+      closedWorld.forEachStrictSubclassOf(use, (ClassElement subclass) {
         if (isNativeOrExtendsNative(subclass)) {
           if (result == null) result = new Set<ClassElement>();
           result.add(subclass);
         }
       });
     }
     return result;
   }
 
   bool operatorEqHandlesNullArgument(FunctionElement operatorEqfunction) {
@@ skipping 2249 matching lines @@
 
   @override
   void onImpactUsed(ImpactUseCase impactUse) {
     if (impactUse == DeferredLoadTask.IMPACT_USE && !supportSerialization) {
       // TODO(johnniwinther): Allow emptying when serialization has been
       // performed.
       resolution.emptyCache();
     }
   }
 }