Remove JavaScriptBackend from ClosedWorldBase

tests/compiler/dart2js/kernel/closed_world2_test.dart

 // Copyright (c) 2017, 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.
 
 // Partial test that the closed world computed from [WorldImpact]s derived from
 // kernel is equivalent to the original computed from resolution.
 library dart2js.kernel.closed_world2_test;
 
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/closure.dart';
@@ skipping 52 matching lines @@
         entryPoint: entryPoint,
         memorySourceFiles: memorySourceFiles,
         options: [
           Flags.analyzeAll,
           Flags.useKernel,
           Flags.enableAssertMessage
         ]);
     ElementResolutionWorldBuilder.useInstantiationMap = true;
     compiler.resolution.retainCachesForTesting = true;
     await compiler.run(entryPoint);
-    compiler.resolutionWorldBuilder.closeWorld(compiler.reporter);
+    compiler.resolutionWorldBuilder.closeWorld();
 
     KernelWorldBuilder worldBuilder = new KernelWorldBuilder(
         compiler.reporter, compiler.backend.kernelTask.program);
     List list = createKernelResolutionEnqueuerListener(compiler.options,
         compiler.reporter, compiler.deferredLoadTask, worldBuilder);
     ResolutionEnqueuerListener resolutionEnqueuerListener = list[0];
     ImpactTransformer impactTransformer = list[1];
     ResolutionEnqueuer enqueuer = new ResolutionEnqueuer(
         compiler.enqueuer,
         compiler.options,
@@ skipping 207 matching lines @@
   final MemberEntity element;
 
   KernelWorkItem(this._worldBuilder, this._impactTransformer, this.element);
 
   @override
   WorldImpact run() {
     ResolutionImpact impact = _worldBuilder.computeWorldImpact(element);
     return _impactTransformer.transformResolutionImpact(impact);
   }
 }