11 files declare their use of RouteSubscriberBase in Zircon Profile 8

AdminRouteSubscriber.php in core/modules/system/src/EventSubscriber/AdminRouteSubscriber.php

Contains \Drupal\system\EventSubscriber\AdminRouteSubscriber.

ContentTranslationRouteSubscriber.php in core/modules/content_translation/src/Routing/ContentTranslationRouteSubscriber.php

Contains \Drupal\content_translation\Routing\ContentTranslationRouteSubscriber.

ModuleRouteSubscriber.php in core/lib/Drupal/Core/EventSubscriber/ModuleRouteSubscriber.php

Contains \Drupal\Core\EventSubscriber\ModuleRouteSubscriber.

NodeAdminRouteSubscriber.php in core/modules/node/src/EventSubscriber/NodeAdminRouteSubscriber.php

Contains \Drupal\node\EventSubscriber\NodeAdminRouteSubscriber.

ResourceRoutes.php in core/modules/rest/src/Routing/ResourceRoutes.php

Contains \Drupal\rest\Routing\ResourceRoutes.

RouteSubscriber.php in core/modules/views/src/EventSubscriber/RouteSubscriber.php

Contains \Drupal\views\EventSubscriber\RouteSubscriber.

RouteSubscriber.php in core/modules/node/src/Routing/RouteSubscriber.php

Contains \Drupal\node\Routing\RouteSubscriber.

RouteSubscriber.php in core/modules/config_translation/src/Routing/RouteSubscriber.php

Contains \Drupal\config_translation\Routing\RouteSubscriber.

RouteSubscriber.php in core/modules/field_ui/src/Routing/RouteSubscriber.php

Contains \Drupal\field_ui\Routing\RouteSubscriber.

RouteTestSubscriber.php in core/modules/system/tests/modules/router_test_directory/src/RouteTestSubscriber.php

Contains \Drupal\router_test\RouteTestSubscriber.

SpecialAttributesRouteSubscriber.php in core/lib/Drupal/Core/EventSubscriber/SpecialAttributesRouteSubscriber.php

Contains \Drupal\Core\EventSubscriber\SpecialAttributesRouteSubscriber.