fix(WebWorker): Return boolean from dispatchRenderEvent

Update web_worker `dispatchRenderEvent` to return a boolean, which
[view.ts](https://github.com/angular/angular/blob/master/modules/angular2/src/core/render/dom/view/view.ts#L85) expects.

modules/angular2/test/core/render/dom/dom_testbed.ts

@@ -52,7 +52,7 @@ class LoggingEventDispatcher implements RenderEventDispatcher {
 
   constructor(log: List<List<any>>) { this.log = log; }
 
-  dispatchRenderEvent(elementIndex: number, eventName: string, locals: Map<string, any>) {
+  dispatchRenderEvent(elementIndex: number, eventName: string, locals: Map<string, any>): boolean {
     this.log.push([elementIndex, eventName, locals]);
     return true;
   }