Move closed world reasoning methods from ClassWorld to ClosedWorld.

pkg/compiler/lib/src/js_backend/field_naming_mixin.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.
 
 part of js_backend.namer;
 
 abstract class _MinifiedFieldNamer implements Namer {
   _FieldNamingRegistry get fieldRegistry;
 
   // Returns a minimal name for the field that is globally unique along
@@ skipping 100 matching lines @@
 
   /// The number of locally used fields. Depending on the naming source
   /// (e.g. inheritance based or globally unique for mixixns) this
   /// might be different from [inheritanceBasedFieldNameCounter].
   int get _localFieldNameCounter => _fieldNameCounter;
   void set _localFieldNameCounter(int val) {
     _fieldNameCounter = val;
   }
 
   factory _FieldNamingScope.forClass(
-      ClassElement cls, ClassWorld world, _FieldNamingRegistry registry) {
+      ClassElement cls, ClosedWorld world, _FieldNamingRegistry registry) {
     _FieldNamingScope result = registry.scopes[cls];
     if (result != null) return result;
 
     if (world.isUsedAsMixin(cls)) {
       result = new _MixinFieldNamingScope.mixin(cls, registry);
     } else {
       if (cls.superclass == null) {
         result = new _FieldNamingScope.rootScope(cls, registry);
       } else {
         _FieldNamingScope superScope =
@@ skipping 95 matching lines @@
       : super.rootScope(box, registry);
 
   @override
   bool containsField(_) => true;
 
   jsAst.Name operator [](Element field) {
     if (!names.containsKey(field)) add(field);
     return names[field];
   }
 }