fixes #168, dart:js implementation with a test

lib/runtime/dart/_isolate_helper.js

 dart_library.library('dart/_isolate_helper', null, /* Imports */[
   "dart_runtime/dart",
   'dart/core',
   'dart/_interceptors',
   'dart/_js_helper',
   'dart/isolate',
   'dart/_foreign_helper',
   'dart/collection',
   'dart/async'
 ], /* Lazy imports */[
@@ skipping 488 matching lines @@
       let isWorkerDefined = exports.globalWorker != null;
       this.isWorker = !dart.notNull(isWindowDefined) && dart.notNull(exports.globalPostMessageDefined);
       this.supportsWorkers = dart.notNull(this.isWorker) || dart.notNull(isWorkerDefined) && IsolateNatives.thisScript != null;
       this.fromCommandLine = !dart.notNull(isWindowDefined) && !dart.notNull(this.isWorker);
     }
     [_nativeInitWorkerMessageHandler]() {
       let func = function(f, a) {
         return function(e) {
           f(a, e);
         };
-      }(_foreign_helper.DART_CLOSURE_TO_JS(IsolateNatives._processWorkerMessage), this.mainManager);
+      }(IsolateNatives._processWorkerMessage, this.mainManager);
       self.onmessage = func;
       self.dartPrint = self.dartPrint || function(serialize) {
         return function(object) {
           if (self.console && self.console.log) {
             self.console.log(object);
           } else {
             self.postMessage(serialize(object));
           }
         };
-      }(_foreign_helper.DART_CLOSURE_TO_JS(_Manager._serializePrintMessage));
+      }(_Manager._serializePrintMessage);
     }
     static _serializePrintMessage(object) {
       return _serializeMessage(dart.map({command: "print", msg: object}));
     }
     maybeCloseWorker() {
       if (dart.notNull(this.isWorker) && dart.notNull(this.isolates.isEmpty) && this.topEventLoop[_activeJsAsyncCount] == 0) {
         this.mainManager.postMessage(_serializeMessage(dart.map({command: 'close'})));
       }
     }
   }
@@ skipping 643 matching lines @@
       }
     }
     static _spawnWorker(functionName, uri, args, message, isSpawnUri, startPaused, replyPort, onError) {
       if (uri == null)
         uri = IsolateNatives.thisScript;
       let worker = new Worker(uri);
       let onerrorTrampoline = function(f, u, c) {
         return function(e) {
           return f(e, u, c);
         };
-      }(_foreign_helper.DART_CLOSURE_TO_JS(IsolateNatives.workerOnError), uri, onError);
+      }(IsolateNatives.workerOnError, uri, onError);
       worker.onerror = onerrorTrampoline;
       let processWorkerMessageTrampoline = function(f, a) {
         return function(e) {
           e.onerror = null;
           return f(a, e);
         };
-      }(_foreign_helper.DART_CLOSURE_TO_JS(IsolateNatives._processWorkerMessage), worker);
+      }(IsolateNatives._processWorkerMessage, worker);
       worker.onmessage = processWorkerMessageTrampoline;
       let o = exports._globalState;
       let workerId = o.nextManagerId;
       o.nextManagerId = dart.notNull(workerId) + 1;
       IsolateNatives.workerIds.set(worker, workerId);
       exports._globalState.managers.set(workerId, worker);
       worker.postMessage(_serializeMessage(dart.map({command: 'start', id: workerId, replyTo: _serializeMessage(replyPort), args: args, msg: _serializeMessage(message), isSpawnUri: isSpawnUri, startPaused: startPaused, functionName: functionName})));
     }
     static workerOnError(event, uri, onError) {
       event.preventDefault();
@@ skipping 251 matching lines @@
         exports._globalState.topEventLoop.enqueue(exports._globalState.currentContext, internalCallback, 'timer');
         this[_inEventLoop] = true;
       } else if (dart.notNull(hasTimer())) {
         let internalCallback = () => {
           this[_handle] = null;
           leaveJsAsync();
           callback();
         };
         dart.fn(internalCallback, dart.void, []);
         enterJsAsync();
-        this[_handle] = self.setTimeout(_js_helper.convertDartClosureToJS(internalCallback, 0), milliseconds);
+        this[_handle] = self.setTimeout(internalCallback, milliseconds);
       } else {
         dart.assert(dart.notNull(milliseconds) > 0);
         throw new core.UnsupportedError("Timer greater than 0.");
       }
     }
     periodic(milliseconds, callback) {
       this[_once] = false;
       this[_inEventLoop] = false;
       this[_handle] = null;
       if (dart.notNull(hasTimer())) {
         enterJsAsync();
-        this[_handle] = self.setInterval(_js_helper.convertDartClosureToJS(dart.fn(() => {
+        this[_handle] = self.setInterval(dart.fn(() => {
           callback(this);
-        }), 0), milliseconds);
+        }), milliseconds);
       } else {
         throw new core.UnsupportedError("Periodic timer.");
       }
     }
     cancel() {
       if (dart.notNull(hasTimer())) {
         if (dart.notNull(this[_inEventLoop])) {
           throw new core.UnsupportedError("Timer in event loop cannot be canceled.");
         }
         if (this[_handle] == null)
@@ skipping 67 matching lines @@
   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;
 });