Split backend implementation of EnqueuerListener

pkg/compiler/lib/src/js_emitter/main_call_stub_generator.dart

 // Copyright (c) 2014, 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.js_emitter.main_call_stub_generator;
 
 import 'package:js_runtime/shared/embedded_names.dart' as embeddedNames;
 
 import '../elements/entities.dart';
 import '../js/js.dart' as jsAst;
@@ skipping 18 matching lines @@
     jsAst.Expression mainAccess =
         emitterTask.isolateStaticClosureAccess(appMain);
     // Since we pass the closurized version of the main method to
     // the isolate method, we must make sure that it exists.
     return js('function(a){ #(#, a); }',
         [emitterTask.staticFunctionAccess(isolateMain), mainAccess]);
   }
 
   jsAst.Statement generateInvokeMain(FunctionEntity main) {
     jsAst.Expression mainCallClosure = null;
-    if (backend.hasIsolateSupport) {
+    if (backend.backendUsage.isIsolateInUse) {
       FunctionEntity isolateMain = helpers.startRootIsolate;
       mainCallClosure = _buildIsolateSetupClosure(main, isolateMain);
     } else {
       mainCallClosure = emitterTask.staticFunctionAccess(main);
     }
 
     jsAst.Expression currentScriptAccess =
         emitterTask.generateEmbeddedGlobalAccess(embeddedNames.CURRENT_SCRIPT);
 
     // This code finds the currently executing script by listening to the
@@ skipping 32 matching lines @@
         } else {
           #mainCallClosure([]);
         }
       })''',
         {
           'currentScript': currentScriptAccess,
           'mainCallClosure': mainCallClosure
         });
   }
 }