| FirebaseInstanceId | Firebase Instance ID provides a unique identifier for each app instance and a mechanism to authenticate and authorize actions (example: sending FCM messages). |
| FirebaseInstanceIdInternalReceiver | Internal receiver for FirebaseInstanceId used to start services securely. |
| FirebaseInstanceIdReceiver | WakefulBroadcastReceiver that receives FirebaseInstanceId and FirebaseMessaging events
and delivers them to the application-specific FirebaseInstanceIdService subclass. |
| FirebaseInstanceIdService | Base class to handle Firebase Instance ID token refresh events. |