Create SsaBuilderTask stub for KernelBackendStrategy

pkg/compiler/lib/src/ssa/ssa.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 ssa;
 
 import '../common/codegen.dart' show CodegenWorkItem;
-import '../common/tasks.dart' show CompilerTask;
-import '../elements/elements.dart' show Element, FunctionElement;
+import '../common/tasks.dart' show CompilerTask, Measurer;
+import '../elements/elements.dart' show MethodElement;
+import '../elements/entities.dart' show MemberEntity;
 import '../io/source_information.dart';
 import '../js/js.dart' as js;
 import '../js_backend/backend.dart' show JavaScriptBackend, FunctionCompiler;
-import '../js_backend/element_strategy.dart' show ElementCodegenWorkItem;
 import '../world.dart' show ClosedWorld;
 
-import 'builder.dart';
-import 'builder_kernel.dart';
 import 'codegen.dart';
 import 'nodes.dart';
 import 'optimize.dart';
 
 class SsaFunctionCompiler implements FunctionCompiler {
   final SsaCodeGeneratorTask generator;
   final SsaBuilderTask _builder;
   final SsaOptimizerTask optimizer;
   final JavaScriptBackend backend;
 
-  SsaFunctionCompiler(JavaScriptBackend backend,
-      SourceInformationStrategy sourceInformationFactory, bool useKernel)
+  SsaFunctionCompiler(JavaScriptBackend backend, Measurer measurer,
+      SourceInformationStrategy sourceInformationFactory)
       : generator = new SsaCodeGeneratorTask(backend, sourceInformationFactory),
-        _builder = useKernel
-            ? new SsaKernelBuilderTask(backend, sourceInformationFactory)
-            : new SsaAstBuilderTask(backend, sourceInformationFactory),
+        _builder = backend.compiler.backendStrategy
+            .createSsaBuilderTask(backend, sourceInformationFactory),
         optimizer = new SsaOptimizerTask(backend),
         backend = backend;
 
   /// Generates JavaScript code for `work.element`.
   /// Using the ssa builder, optimizer and codegenerator.
-  js.Fun compile(ElementCodegenWorkItem work, ClosedWorld closedWorld) {
+  js.Fun compile(CodegenWorkItem work, ClosedWorld closedWorld) {
     HGraph graph = _builder.build(work, closedWorld);
     if (graph == null) return null;
     optimizer.optimize(work, graph, closedWorld);
-    Element element = work.element;
+    MemberEntity element = work.element;
     js.Expression result = generator.generateCode(work, graph, closedWorld);
-    if (element is FunctionElement) {
+    if (element is MethodElement) {
       // TODO(sigmund): replace by kernel transformer when `useKernel` is true.
       result = backend.rewriteAsync(element, result);
     }
     return result;
   }
 
   Iterable<CompilerTask> get tasks {
     return <CompilerTask>[_builder, optimizer, generator];
   }
 }
 
 abstract class SsaBuilderTask implements CompilerTask {
   /// Creates the [HGraph] for [work] or returns `null` if no code is needed
   /// for [work].
   HGraph build(CodegenWorkItem work, ClosedWorld closedWorld);
 }