Replace ClosedWorld.backend with ClosedWorld.backendClasses

pkg/compiler/lib/src/js_backend/backend_impact.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.
 
 library dart2js.js_helpers.impact;
 
 import '../common/names.dart';
 import '../compiler.dart' show Compiler;
 import '../core_types.dart' show CommonElements;
 import '../dart_types.dart' show InterfaceType;
@@ skipping 428 matching lines @@
       _lazyField = new BackendImpact(staticUses: [helpers.cyclicThrowHelper]);
     }
     return _lazyField;
   }
 
   BackendImpact _typeLiteral;
 
   BackendImpact get typeLiteral {
     if (_typeLiteral == null) {
       _typeLiteral = new BackendImpact(
-          instantiatedClasses: [backend.typeImplementation],
+          instantiatedClasses: [backend.backendClasses.typeImplementation],
           staticUses: [helpers.createRuntimeType]);
     }
     return _typeLiteral;
   }
 
   BackendImpact _stackTraceInCatch;
 
   BackendImpact get stackTraceInCatch {
     if (_stackTraceInCatch == null) {
       _stackTraceInCatch = new BackendImpact(
@@ skipping 166 matching lines @@
             helpers.jsJavaScriptFunctionClass
           ],
           features: new EnumSet<BackendFeature>.fromValues([
             BackendFeature.needToInitializeDispatchProperty,
             BackendFeature.needToInitializeIsolateAffinityTag
           ], fixed: true));
     }
     return _interceptorUse;
   }
 }