Replace ClosedWorld.backend with ClosedWorld.backendClasses

pkg/compiler/lib/src/constant_system_dart.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 dart2js.constant_system.dart;
 
 import 'compiler.dart' show Compiler;
 import 'constants/constant_system.dart';
 import 'constants/values.dart';
 import 'dart_types.dart';
@@ skipping 428 matching lines @@
   MapConstantValue createMap(Compiler compiler, InterfaceType type,
       List<ConstantValue> keys, List<ConstantValue> values) {
     return new MapConstantValue(type, keys, values);
   }
 
   @override
   ConstantValue createType(Compiler compiler, DartType type) {
     // TODO(johnniwinther): Change the `Type` type to
     // `compiler.coreTypes.typeType` and check the backend specific value in
     // [checkConstMapKeysDontOverrideEquals] in 'members.dart'.
-    return new TypeConstantValue(type,
-        compiler.backend.typeImplementation.computeType(compiler.resolution));
+    return new TypeConstantValue(
+        type,
+        compiler.backend.backendClasses.typeImplementation
+            .computeType(compiler.resolution));
   }
 
   @override
   ConstantValue createSymbol(Compiler compiler, String text) {
     throw new UnsupportedError('DartConstantSystem.evaluate');
   }
 
   bool isInt(ConstantValue constant) => constant.isInt;
   bool isDouble(ConstantValue constant) => constant.isDouble;
   bool isString(ConstantValue constant) => constant.isString;
   bool isBool(ConstantValue constant) => constant.isBool;
   bool isNull(ConstantValue constant) => constant.isNull;
 
   bool isSubtype(DartTypes types, DartType s, DartType t) {
     return types.isSubtype(s, t);
   }
 }