Split backend implementation of EnqueuerListener

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 72 matching lines @@
     compiler.resolutionWorldBuilder.closeWorld(compiler.reporter);
 
     JavaScriptBackend backend = compiler.backend;
     // Create a new resolution enqueuer and feed it with the [WorldImpact]s
     // computed from kernel through the [build] in `kernel_impact.dart`.
     ResolutionEnqueuer enqueuer = new ResolutionEnqueuer(
         compiler.enqueuer,
         compiler.options,
         compiler.reporter,
         const TreeShakingEnqueuerStrategy(),
-        backend,
+        backend.resolutionEnqueuerListener,
         backend.nativeResolutionEnqueuer(),
         new ResolutionWorldBuilderImpl(
             compiler.backend, compiler.resolution, const OpenWorldStrategy()),
         new ResolutionWorkItemBuilder(compiler.resolution),
         'enqueuer from kernel');
     ClosedWorld closedWorld = computeClosedWorld(compiler, enqueuer);
 
-    checkResolutionEnqueuers(compiler.backend, compiler.backend,
-        compiler.enqueuer.resolution, enqueuer,
+    checkResolutionEnqueuers(compiler.backend.backendUsage,
+        compiler.backend.backendUsage, compiler.enqueuer.resolution, enqueuer,
         typeEquivalence: (ResolutionDartType a, ResolutionDartType b) {
       return areTypesEquivalent(unalias(a), unalias(b));
     }, elementFilter: (Element element) {
       if (element is ConstructorElement && element.isRedirectingFactory) {
         // Redirecting factory constructors are skipped in kernel.
         return false;
       }
       if (element is ClassElement) {
         for (ConstructorElement constructor in element.constructors) {
           if (!constructor.isRedirectingFactory) {
@@ skipping 29 matching lines @@
       backend.computeMainImpact(compiler.mainFunction, forResolution: true));
   enqueuer.forEach((work) {
     AstElement element = work.element;
     ResolutionImpact resolutionImpact = build(compiler, element.resolvedAst);
     WorldImpact worldImpact = compiler.backend.impactTransformer
         .transformResolutionImpact(enqueuer, resolutionImpact);
     enqueuer.applyImpact(worldImpact, impactSource: element);
   });
   return enqueuer.worldBuilder.closeWorld(compiler.reporter);
 }