gms Task to rx Observable

fun <TResult> Task<TResult>.asObservable(): Observable<TResult> {
  return Observable.create<TResult> { emitter ->
    this.addOnSuccessListener {
      emitter.onNext(it)
      emitter.onComplete()
    }
    this.addOnFailureListener {
      emitter.onError(it)
    }
  }
}