Add support for compiling Dart via the FE in dart2js.

tests/compiler/dart2js/kernel/impact_test.dart

 // Copyright (c) 2016, 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.impact_test;
 
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/commandline_options.dart';
 import 'package:compiler/src/common.dart';
 import 'package:compiler/src/common/names.dart';
@@ skipping 721 matching lines @@
   bool fullTest = args.contains('--full');
   asyncTest(() async {
     enableDebugMode();
     Uri entryPoint =
         Uri.parse('memory:sdk/tests/compiler/dart2js_native/main.dart');
     Compiler compiler = compilerFor(
         entryPoint: entryPoint,
         memorySourceFiles: SOURCE,
         options: [
           fullTest ? Flags.analyzeAll : Flags.analyzeOnly,
-          Flags.useKernel,
+          Flags.useKernelInSsa,
           Flags.enableAssertMessage
         ]);
     compiler.resolution.retainCachesForTesting = true;
     Expect.isTrue(await compiler.run(entryPoint));
     JavaScriptBackend backend = compiler.backend;
     KernelToElementMapForImpact kernelElementMap =
         new KernelToElementMapForImpactImpl(
             compiler.reporter, compiler.environment);
     kernelElementMap.addProgram(backend.kernelTask.program);
 
@@ skipping 150 matching lines @@
         builder.registerFeature(Feature.THROW_EXPRESSION);
         break;
       default:
         builder.registerFeature(feature);
         break;
     }
   }
   impact.nativeData.forEach(builder.registerNativeData);
   return builder;
 }