Use JsStrategy, remove KernelBackendStrategy

pkg/compiler/lib/src/kernel/kernel_strategy.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.
 
 library dart2js.kernel.frontend_strategy;
 
 import '../closure.dart';
 import '../common.dart';
 import '../common_elements.dart';
 import '../common/backend_api.dart';
@@ skipping 19 matching lines @@
 import '../native/resolver.dart';
 import '../options.dart';
 import '../serialization/task.dart';
 import '../patch_parser.dart';
 import '../resolved_uri_translator.dart';
 import '../universe/world_builder.dart';
 import '../universe/world_impact.dart';
 import '../world.dart';
 import 'element_map.dart';
 import 'element_map_impl.dart';
-import 'kernel_backend_strategy.dart';
 
 /// Front end strategy that loads '.dill' files and builds a resolved element
 /// model from kernel IR nodes.
 class KernelFrontEndStrategy extends FrontendStrategyBase {
   CompilerOptions _options;
   KernelToElementMapForImpactImpl _elementMap;
 
   KernelAnnotationProcessor _annotationProcesser;
 
   KernelFrontEndStrategy(
       this._options, DiagnosticReporter reporter, env.Environment environment)
-      : _elementMap = useJsStrategyForTesting
-            ? new KernelToElementMapForImpactImpl2(reporter, environment)
-            : new KernelToElementMapImpl(reporter, environment);
+      : _elementMap =
+            new KernelToElementMapForImpactImpl(reporter, environment);
 
   @override
   LibraryLoaderTask createLibraryLoader(
       ResolvedUriTranslator uriTranslator,
       ScriptLoader scriptLoader,
       ElementScanner scriptScanner,
       LibraryDeserializer deserializer,
       PatchResolverFunction patchResolverFunc,
       PatchParserTask patchParser,
       env.Environment environment,
@@ skipping 166 matching lines @@
   int get preMirrorsMethodCount {
     // TODO(redemption): Implement this.
     return null;
   }
 
   @override
   void onQueueEmpty(Enqueuer enqueuer, Iterable<ClassEntity> recentClasses) {
     // TODO(redemption): Implement this.
   }
 }