object FirebasePushUpdates : PushUpdates {

    val jobSubject = PublishSubject.create<Job>().toSerialized()

    override val jobs: Observable<Job> = jobSubject

}

class FirebaseMessagingService : FirebaseMessagingService() {

    override fun onMessageReceived(remoteMessage: RemoteMessage) {
        val job = parseJob(removeMessage.data)
        FirebasePushUpdates.jobSubject.onNext(job)
    }

    private fun parseJob(data: String) : Job {
        // ...
    }

}

class MergePushUpdates(pushUpdates: List<PushUpdates>) : PushUpdates {

    override val jobs: Observable<Job> =
            Observable.merge(pushUpdates.map { it.jobs })

}