remove #177 workaround

lib/runtime/dart/_isolate_helper.js

 var _isolate_helper = dart.defineLibrary(_isolate_helper, {});
 var core = dart.import(core);
 var _native_typed_data = dart.import(_native_typed_data);
 var _interceptors = dart.lazyImport(_interceptors);
 var _js_helper = dart.lazyImport(_js_helper);
 var isolate = dart.import(isolate);
 var _foreign_helper = dart.import(_foreign_helper);
 var _js_embedded_names = dart.import(_js_embedded_names);
 var collection = dart.import(collection);
 var async = dart.import(async);
@@ skipping 760 matching lines @@
       if (event == null) {
         this.checkOpenReceivePortsFromCommandLine();
         exports._globalState.maybeCloseWorker();
         return false;
       }
       event.process();
       return true;
     }
     [_runHelper]() {
       if (exports.globalWindow != null) {
+        // Function next: () → dynamic
         let next = (() => {
           if (!dart.notNull(this.runIteration()))
             return;
-          async.Timer.run(dart.as(next, __CastType2));
+          async.Timer.run(next);
         }).bind(this);
-        dart.dcall(next);
+        next();
       } else {
         while (this.runIteration()) {
         }
       }
     }
     run() {
       if (!dart.notNull(exports._globalState.isWorker)) {
         this[_runHelper]();
       } else {
         try {
@@ skipping 577 matching lines @@
       if (core.identical(other, this))
         return true;
       if (dart.is(other, CapabilityImpl)) {
         return core.identical(this[_id], other[_id]);
       }
       return false;
     }
   }
   CapabilityImpl[dart.implements] = () => [isolate.Capability];
   dart.defineNamedConstructor(CapabilityImpl, '_internal');
-  let __CastType2 = dart.typedef('__CastType2', () => dart.functionType(dart.void, []));
   // Exports:
   exports.enterJsAsync = enterJsAsync;
   exports.leaveJsAsync = leaveJsAsync;
   exports.isWorker = isWorker;
   exports.startRootIsolate = startRootIsolate;
   exports.IsolateNatives = IsolateNatives;
   exports.RawReceivePortImpl = RawReceivePortImpl;
   exports.ReceivePortImpl = ReceivePortImpl;
   exports.TimerImpl = TimerImpl;
   exports.hasTimer = hasTimer;
   exports.CapabilityImpl = CapabilityImpl;
 })(_isolate_helper, core, _native_typed_data, _interceptors, _js_helper, isolate, _foreign_helper, _js_embedded_names, collection, async);