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/src/core/render/api.ts

@@ -510,6 +510,7 @@ export interface RenderEventDispatcher {
    * Called when an event was triggered for a on-* attribute on an element.
    * @param {Map<string, any>} locals Locals to be used to evaluate the
    *   event expressions
+   * @return {boolean} False if `preventDefault` should be called on the DOM event.
    */
-  dispatchRenderEvent(elementIndex: number, eventName: string, locals: Map<string, any>);
+  dispatchRenderEvent(elementIndex: number, eventName: string, locals: Map<string, any>): boolean;
 }