queueObserverIfProtocolIsNotBroken (observer) {
    if (this.isBroken()) {
      this.notifyFatalErrorToObserver(observer)
      return false
    }

    return this._responseHandler._queueObserver(observer)
  }
Enqueue the observer if the protocol is not broken.
In case it's broken, the observer will be notified about the error.

@param {StreamObserver} observer The observer
@returns {boolean} if it was queued