Remove BackendClasses and JavaScriptBackendClasses.

pkg/compiler/lib/src/elements/elements.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 elements;
 
 import 'package:front_end/src/fasta/parser/async_modifier.dart'
     show AsyncModifier;
 
 import '../common.dart';
@@ skipping 760 matching lines @@
   }
 
   static bool isConstructorOfTypedArraySubclass(
       Element element, ClosedWorld closedWorld) {
     if (closedWorld.commonElements.typedDataLibrary == null) return false;
     if (!element.isConstructor) return false;
     ConstructorElement constructor = element.implementation;
     constructor = constructor.effectiveTarget;
     ClassElement cls = constructor.enclosingClass;
     return cls.library == closedWorld.commonElements.typedDataLibrary &&
-        closedWorld.backendClasses.isNativeClass(cls) &&
+        closedWorld.nativeData.isNativeClass(cls) &&
         closedWorld.isSubtypeOf(
             cls, closedWorld.commonElements.typedDataClass) &&
         closedWorld.isSubtypeOf(cls, closedWorld.commonElements.listClass) &&
         constructor.name == '';
   }
 
   static bool switchStatementHasContinue(
       SwitchStatement node, TreeElements elements) {
     for (SwitchCase switchCase in node.cases) {
       for (Node labelOrCase in switchCase.labelsAndCases) {
@@ skipping 1241 matching lines @@
   /// by a field.
   bool get isDeclaredByField;
 
   /// Returns `true` if this member is abstract.
   bool get isAbstract;
 
   /// If abstract, [implementation] points to the overridden concrete member,
   /// if any. Otherwise [implementation] points to the member itself.
   Member get implementation;
 }