Add support for compiling Dart via the FE in dart2js.

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, CodegenRegistry;
 import '../common/tasks.dart' show CompilerTask, Measurer;
 import '../constants/values.dart';
 import '../elements/elements.dart' show MethodElement;
@@ skipping 28 matching lines @@
 
   /// Generates JavaScript code for `work.element`.
   /// Using the ssa builder, optimizer and codegenerator.
   js.Fun compile(CodegenWorkItem work, ClosedWorld closedWorld) {
     HGraph graph = _builder.build(work, closedWorld);
     if (graph == null) return null;
     optimizer.optimize(work, graph, closedWorld);
     MemberEntity element = work.element;
     js.Expression result = generator.generateCode(work, graph, closedWorld);
     if (element is MethodElement) {
-      // TODO(sigmund): replace by kernel transformer when `useKernel` is true.
+      // TODO(sigmund): replace by kernel transformer when `useKernelInSsa` is
+      // true.
       result =
           backend.rewriteAsync(closedWorld.commonElements, element, result);
     }
     return result;
   }
 
   Iterable<CompilerTask> get tasks {
     return <CompilerTask>[_builder, optimizer, generator];
   }
 }
@@ skipping 57 matching lines @@
         // the static variable.
         // We also need to register the use of the cyclic-error helper.
         registry.worldImpact.registerStaticUse(new StaticUse.staticInvoke(
             closedWorld.commonElements.cyclicThrowHelper,
             CallStructure.ONE_ARG));
       }
     }
     return false;
   }
 }