Add support for compiling Dart via the FE in dart2js.

pkg/compiler/lib/src/js_backend/resolution_listener.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 js_backend.backend.resolution_listener;
 
 import '../common/names.dart' show Identifiers, Uris;
 import '../common_elements.dart' show CommonElements, ElementEnvironment;
 import '../constants/values.dart';
 import '../deferred_load.dart';
@@ skipping 210 matching lines @@
         (_noSuchMethodRegistry.hasThrowingNoSuchMethod ||
             _noSuchMethodRegistry.hasComplexNoSuchMethod)) {
       _backendUsage.processBackendImpact(_impacts.noSuchMethodSupport);
       enqueuer.applyImpact(
           _impacts.noSuchMethodSupport.createImpact(_elementEnvironment));
       _backendUsage.isNoSuchMethodUsed = true;
     }
 
     if (!enqueuer.queueIsEmpty) return false;
 
-    if (_options.useKernel) {
+    if (!_options.previewDart2 && _options.useKernel) {
       _kernelTask?.buildKernelIr();
     }
 
     _mirrorsAnalysis.onQueueEmpty(enqueuer, recentClasses);
     return true;
   }
 
   @override
   void onQueueClosed() {}
 
@@ skipping 257 matching lines @@
     }
     _registerBackendImpact(
         impactBuilder, new BackendImpact(globalUses: staticUses));
   }
 
   @override
   void logSummary(void log(String message)) {
     _nativeEnqueuer.logSummary(log);
   }
 }