Use backend-specific enqueuer.

pkg/compiler/lib/src/js_backend/backend.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 js_backend.backend;
 
 import 'dart:async' show Future;
 
 import 'package:js_runtime/shared/embedded_names.dart' as embeddedNames;
 
 import '../closure.dart';
 import '../common.dart';
 import '../common/backend_api.dart'
     show Backend, ImpactTransformer, ForeignResolver, NativeRegistry;
 import '../common/codegen.dart' show CodegenImpact, CodegenWorkItem;
 import '../common/names.dart' show Identifiers, Selectors, Uris;
 import '../common/registry.dart' show EagerRegistry, Registry;
 import '../common/resolution.dart' show Frontend, Resolution, ResolutionImpact;
 import '../common/tasks.dart' show CompilerTask;
 import '../common/work.dart' show ItemCompilationContext;
 import '../compiler.dart' show Compiler;
 import '../constants/constant_system.dart';
 import '../constants/expressions.dart';
 import '../constants/values.dart';
 import '../core_types.dart' show CoreClasses, CoreTypes;
 import '../dart_types.dart';
 import '../deferred_load.dart' show DeferredLoadTask;
 import '../dump_info.dart' show DumpInfoTask;
 import '../elements/elements.dart';
-import '../enqueue.dart' show Enqueuer, ResolutionEnqueuer;
+import '../enqueue.dart'
+    show Enqueuer, ResolutionEnqueuer, TreeShakingEnqueuerStrategy;
 import '../io/position_information.dart' show PositionSourceInformationStrategy;
 import '../io/source_information.dart' show SourceInformationStrategy;
 import '../io/start_end_information.dart'
     show StartEndSourceInformationStrategy;
 import '../js/js.dart' as jsAst;
 import '../js/js.dart' show js;
 import '../js/js_source_mapping.dart' show JavaScriptSourceInformationStrategy;
 import '../js/rewrite_async.dart';
 import '../js_emitter/js_emitter.dart' show CodeEmitterTask;
 import '../library_loader.dart' show LibraryLoader, LoadedLibraries;
@@ skipping 16 matching lines @@
         WorldImpact,
         WorldImpactVisitor;
 import '../util/util.dart';
 import '../world.dart' show ClassWorld;
 import 'backend_helpers.dart';
 import 'backend_impact.dart';
 import 'backend_serialization.dart' show JavaScriptBackendSerialization;
 import 'checked_mode_helpers.dart';
 import 'constant_handler_javascript.dart';
 import 'custom_elements_analysis.dart';
+import 'enqueuer.dart';
 import 'js_interop_analysis.dart' show JsInteropAnalysis;
 import 'lookup_map_analysis.dart' show LookupMapAnalysis;
 import 'namer.dart';
 import 'native_data.dart' show NativeData;
 import 'no_such_method_registry.dart';
 import 'patch_resolver.dart';
 import 'type_variable_handler.dart';
 
 part 'runtime_types.dart';
 
@@ skipping 316 matching lines @@
 
   TypeMask _unmodifiableArrayTypeCache;
   TypeMask get unmodifiableArrayType {
     if (_unmodifiableArrayTypeCache == null) {
       _unmodifiableArrayTypeCache = new TypeMask.nonNullExact(
           helpers.jsUnmodifiableArrayClass, compiler.world);
     }
     return _fixedArrayTypeCache;
   }
 
-
   /// Maps special classes to their implementation (JSXxx) class.
   Map<ClassElement, ClassElement> implementationClasses;
 
   bool needToInitializeIsolateAffinityTag = false;
   bool needToInitializeDispatchProperty = false;
 
   final Namer namer;
 
   /**
    * A collection of selectors that must have a one shot interceptor
@@ skipping 1142 matching lines @@
       enqueueType(enqueuer, type, registry);
     }
     for (ClassElement cls in impact.instantiatedClasses) {
       enqueueClass(enqueuer, cls, registry);
     }
     for (BackendImpact otherImpact in impact.otherImpacts) {
       enqueueImpact(enqueuer, otherImpact, registry);
     }
   }
 
+  CodegenEnqueuer createCodegenEnqueuer(Compiler compiler) {
+    return new CodegenEnqueuer(compiler, createItemCompilationContext,
+        const TreeShakingEnqueuerStrategy());
+  }
+
   WorldImpact codegen(CodegenWorkItem work) {
     Element element = work.element;
     if (compiler.elementHasCompileTimeError(element)) {
       DiagnosticMessage message =
           // If there's more than one error, the first is probably most
           // informative, as the following errors may be side-effects of the
           // first error.
           compiler.elementsWithCompileTimeErrors[element].first;
       String messageText = message.message.computeMessage();
       jsAst.LiteralString messageLiteral =
@@ skipping 1616 matching lines @@
 
   @override
   void onImpactUsed(ImpactUseCase impactUse) {
     if (impactUse == DeferredLoadTask.IMPACT_USE && !supportSerialization) {
       // TODO(johnniwinther): Allow emptying when serialization has been
       // performed.
       resolution.emptyCache();
     }
   }
 }