Replace ClosedWorld.backend with ClosedWorld.backendClasses

pkg/compiler/lib/src/native/enqueue.dart

 // Copyright (c) 2014, 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.
 
 import 'dart:collection' show Queue;
 
 import '../common.dart';
 import '../common/backend_api.dart' show ForeignResolver;
 import '../common/registry.dart' show Registry;
 import '../common/resolution.dart' show Resolution;
@@ skipping 465 matching lines @@
         } else if (type == coreTypes.numType) {
           backend.registerInstantiatedType(
               coreTypes.doubleType, world, registry);
           backend.registerInstantiatedType(coreTypes.intType, world, registry);
         } else if (type == coreTypes.stringType) {
           backend.registerInstantiatedType(type, world, registry);
         } else if (type == coreTypes.nullType) {
           backend.registerInstantiatedType(type, world, registry);
         } else if (type == coreTypes.boolType) {
           backend.registerInstantiatedType(type, world, registry);
-        } else if (compiler.types
-            .isSubtype(type, backend.listImplementation.rawType)) {
+        } else if (compiler.types.isSubtype(
+            type, backend.backendClasses.listImplementation.rawType)) {
           backend.registerInstantiatedType(type, world, registry);
         }
         // TODO(johnniwinther): Improve spec string precision to handle type
         // arguments and implements relations that preserve generics. Currently
         // we cannot distinguish between `List`, `List<dynamic>`, and
         // `List<int>` and take all to mean `List<E>`; in effect not including
         // any native subclasses of generic classes.
         // TODO(johnniwinther,sra): Find and replace uses of `List` with the
         // actual implementation classes such as `JSArray` et al.
         enqueueUnusedClassesMatching((ClassElement nativeClass) {
@@ skipping 175 matching lines @@
     List<Element> directSubtypes =
         emitter.directSubtypes.putIfAbsent(superclass, () => <ClassElement>[]);
     directSubtypes.add(cls);
   }
 
   void logSummary(log(message)) {
     log('Compiled ${registeredClasses.length} native classes, '
         '${unusedClasses.length} native classes omitted.');
   }
 }