Add ElementCodegenWorldBuilder

pkg/compiler/lib/src/compiler.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 dart2js.compiler_base;
 
 import 'dart:async' show Future;
 
 import '../compiler_new.dart' as api;
 import 'backend_strategy.dart';
@@ skipping 22 matching lines @@
 import 'elements/elements.dart';
 import 'elements/entities.dart';
 import 'elements/resolution_types.dart' show ResolutionDartType, Types;
 import 'elements/types.dart' show DartTypes;
 import 'enqueue.dart' show Enqueuer, EnqueueTask, ResolutionEnqueuer;
 import 'environment.dart';
 import 'frontend_strategy.dart';
 import 'id_generator.dart';
 import 'io/source_information.dart' show SourceInformation;
 import 'js_backend/backend.dart' show JavaScriptBackend;
+import 'js_backend/element_strategy.dart' show ElementBackendStrategy;
 import 'kernel/kernel_strategy.dart';
 import 'library_loader.dart'
     show
         ElementScanner,
         LibraryLoader,
         LibraryLoaderTask,
         LoadedLibraries,
         ScriptLoader;
 import 'mirrors_used.dart' show MirrorUsageAnalyzerTask;
 import 'null_compiler_output.dart' show NullCompilerOutput, NullSink;
@@ skipping 1507 matching lines @@
   _ElementScanner(this.scanner);
   void scanLibrary(LibraryElement library) => scanner.scanLibrary(library);
   void scanUnit(CompilationUnitElement unit) => scanner.scan(unit);
 }
 
 class _EmptyEnvironment implements Environment {
   const _EmptyEnvironment();
 
   String valueOf(String key) => null;
 }