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;
 }

modules/angular2/src/web_workers/ui/event_dispatcher.ts

@@ -17,7 +17,7 @@ export class EventDispatcher implements RenderEventDispatcher {
   constructor(private _viewRef: RenderViewRef, private _sink: EventEmitter,
               private _serializer: Serializer) {}
 
-  dispatchRenderEvent(elementIndex: number, eventName: string, locals: Map<string, any>) {
+  dispatchRenderEvent(elementIndex: number, eventName: string, locals: Map<string, any>): boolean {
     var e = locals.get('$event');
     var serializedEvent;
     // TODO (jteplitz602): support custom events #3350
@@ -106,5 +106,9 @@ export class EventDispatcher implements RenderEventDispatcher {
       "eventName": eventName,
       "locals": serializedLocals
     });
+
+    // TODO(kegluneq): Eventually, we want the user to indicate from the UI side whether the event
+    // should be canceled, but for now just call `preventDefault` on the original DOM event.
+    return false;
   }
 }

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;
   }

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;
   }
 }