The [PostMessageBus](https://github.com/angular/angular/blob/master/modules/angular2/src/web_workers/shared/post_message_bus.ts#L17)'s constructor tries to inject `PostMessageBusSink` and `PostMessageBusSource` but they haven't been defined yet.
The PostMessageBus's constructor tries to inject
PostMessageBusSinkandPostMessageBusSourcebut they haven't been defined yet.