Fix the locals lookup of variables and partial implementation of boxing of variables.

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
   // the given element's class inheritance chain.
   //
   // The inheritance scope based naming might not yield a name. For instance,
   // this could be because the field belongs to a mixin. In such a case this
   // will return `null` and a normal field name has to be used.
   jsAst.Name _minifiedInstanceFieldPropertyName(FieldEntity element) {
     if (_nativeData.hasFixedBackendName(element)) {
       return new StringBackedName(_nativeData.getFixedBackendName(element));
     }
 
     _FieldNamingScope names;
     if (element is BoxFieldElement) {
       names = new _FieldNamingScope.forBox(element.box, fieldRegistry);
-    } else if (element is JBoxedField) {
+    } else if (element is JRecord) {
       names = new _FieldNamingScope.forBox(element.box, fieldRegistry);
     } else {
       ClassEntity cls = element.enclosingClass;
       names = new _FieldNamingScope.forClass(cls, _closedWorld, fieldRegistry);
     }
 
     if (names.containsField(element)) {
       return names[element];
     }
     return null;
@@ skipping 196 matching lines @@
       : super.rootScope(box, registry);
 
   @override
   bool containsField(_) => true;
 
   jsAst.Name operator [](Entity field) {
     if (!names.containsKey(field)) add(field);
     return names[field];
   }
 }