Expanded class hierarchy of FirebaseMessageService in Firebase Push Notification (FCM) 8
- class \Drupal\firebase\Service\FirebaseServiceBase implements FirebaseServiceInterface uses DependencySerializationTrait
- class \Drupal\firebase\Service\FirebaseGroupManagerService
- class \Drupal\firebase\Service\FirebaseMessageService
- class \Drupal\firebase\Service\FirebaseTopicManagerService