Check equivalence of closed world based on kernel elements.

tests/compiler/dart2js/kernel/closed_world_test.dart

 // Copyright (c) 2016, 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.
 
 // Tests that the closed world computed from [WorldImpact]s derived from kernel
 // is equivalent to the original computed from resolution.
 library dart2js.kernel.closed_world_test;
 
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/commandline_options.dart';
@@ skipping 93 matching lines @@
         new KernelWorkItemBuilder(compiler),
         'enqueuer from kernel');
     ClosedWorld closedWorld = computeClosedWorld(
         compiler.reporter, enqueuer, compiler.elementEnvironment);
     BackendUsage backendUsage = backendUsageBuilder.close();
     checkResolutionEnqueuers(
         backendUsage, backendUsage, compiler.enqueuer.resolution, enqueuer,
         typeEquivalence: (ResolutionDartType a, ResolutionDartType b) {
       return areTypesEquivalent(unalias(a), unalias(b));
     }, elementFilter: elementFilter, verbose: arguments.verbose);
-    checkClosedWorlds(
-        compiler.resolutionWorldBuilder.closedWorldForTesting, closedWorld,
+    checkClosedWorlds(compiler.resolutionWorldBuilder.closedWorldForTesting,
+        closedWorld, areElementsEquivalent,
         verbose: arguments.verbose);
   });
 }
 
 bool elementFilter(Entity element) {
   if (element is ConstructorElement && element.isRedirectingFactory) {
     // Redirecting factory constructors are skipped in kernel.
     return false;
   }
   if (element is ClassElement) {
@@ skipping 64 matching lines @@
 
   KernelWorkItem(this._compiler, this._impactTransformer, this.element);
 
   @override
   WorldImpact run() {
     print('$element');
     ResolutionImpact resolutionImpact = build(_compiler, element.resolvedAst);
     return _impactTransformer.transformResolutionImpact(resolutionImpact);
   }
 }