Revert "Remove JavaScriptBackend from ClosedWorldBase"

pkg/compiler/lib/src/universe/world_builder.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 world_builder;
 
 import 'dart:collection';
 
 import '../common.dart';
 import '../common/names.dart' show Identifiers;
 import '../common/resolution.dart' show Resolution;
 import '../common_elements.dart';
 import '../constants/values.dart';
 import '../elements/elements.dart';
 import '../elements/entities.dart';
 import '../elements/resolution_types.dart';
 import '../elements/types.dart';
 import '../js_backend/backend.dart' show JavaScriptBackend;
 import '../js_backend/constant_handler_javascript.dart'
     show JavaScriptConstantCompiler;
 import '../js_backend/native_data.dart' show NativeBasicData;
 import '../universe/class_set.dart';
 import '../universe/function_set.dart' show FunctionSetBuilder;
 import '../util/enumset.dart';
 import '../util/util.dart';
-import '../world.dart'
-    show World, ClosedWorld, ClosedWorldImpl, KernelClosedWorld, OpenWorld;
+import '../world.dart' show World, ClosedWorld, ClosedWorldImpl, OpenWorld;
 import 'selector.dart' show Selector;
 import 'use.dart'
     show
         ConstantUse,
         ConstantUseKind,
         DynamicUse,
         DynamicUseKind,
         StaticUse,
         StaticUseKind;
 
@@ skipping 138 matching lines @@
 
   /// All directly instantiated types, that is, the types of the directly
   /// instantiated classes.
   // TODO(johnniwinther): Improve semantic precision.
   Iterable<InterfaceType> get instantiatedTypes;
 
   /// Registers that [type] is checked in this world builder. The unaliased type
   /// is returned.
   void registerIsCheck(DartType type);
 }