Replace ClosedWorld.backend with ClosedWorld.backendClasses

pkg/compiler/lib/src/js_backend/lookup_map_analysis.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.
 
 /// Analysis to determine how to generate code for `LookupMap`s.
 library compiler.src.js_backend.lookup_map_analysis;
 
 import 'package:pub_semver/pub_semver.dart';
 
 import '../common.dart';
@@ skipping 259 matching lines @@
   /// returned using a type-argument expression.
   void _addGenerics(InterfaceType type) {
     if (!type.isGeneric) return;
     for (var arg in type.typeArguments) {
       if (arg is InterfaceType) {
         _addClassUse(arg.element);
         // Note: this call was needed to generate correct code for
         // type_lookup_map/generic_type_test
         // TODO(sigmund): can we get rid of this?
         backend.computeImpactForInstantiatedConstantType(
-            backend.typeImplementation.rawType, impactBuilder);
+            backend.backendClasses.typeImplementation.rawType, impactBuilder);
         _addGenerics(arg);
       }
     }
   }
 
   /// Callback from the codegen enqueuer, invoked when a constant (which is
   /// possibly a const key or a type literal) is used in the program.
   void registerTypeConstant(ClassElement element) {
     if (!_isEnabled || !_inCodegen) return;
     _addClassUse(element);
@@ skipping 148 matching lines @@
         original.fields[analysis.valueField] = keyValuePairs[1];
       }
     } else {
       original.fields[analysis.entriesField] =
           new ListConstantValue(listType, keyValuePairs);
     }
   }
 }
 
 final _validLookupMapVersionConstraint = new VersionConstraint.parse('^0.0.1');