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/web_workers/worker/event_dispatcher_spec.ts

@@ -69,7 +69,8 @@ export function main() {
 class SpyEventDispatcher implements RenderEventDispatcher {
   constructor(private _callback: Function) {}
 
-  dispatchRenderEvent(elementIndex: number, eventName: string, locals: Map<string, any>) {
+  dispatchRenderEvent(elementIndex: number, eventName: string, locals: Map<string, any>): boolean {
     this._callback(elementIndex, eventName, locals);
+    return false;
   }
 }