18 files declare their use of RouteSubscriberBase

AdminRouteSubscriber.php in core/modules/system/src/EventSubscriber/AdminRouteSubscriber.php
ContentModerationRouteSubscriber.php in core/modules/content_moderation/src/Routing/ContentModerationRouteSubscriber.php
ContentTranslationRouteSubscriber.php in core/modules/content_translation/src/Routing/ContentTranslationRouteSubscriber.php
MenuLinksetRoutes.php in core/modules/system/src/Routing/MenuLinksetRoutes.php
MigrateDrupalUiRouteSubscriber.php in core/modules/migrate_drupal_ui/src/Routing/MigrateDrupalUiRouteSubscriber.php
ModuleRouteSubscriber.php in core/lib/Drupal/Core/EventSubscriber/ModuleRouteSubscriber.php
NodeAdminRouteSubscriber.php in core/modules/node/src/EventSubscriber/NodeAdminRouteSubscriber.php
RouteSubscriber.php in core/modules/serialization/tests/modules/user_route_alter_test/src/Routing/RouteSubscriber.php
RouteSubscriber.php in core/modules/views/src/EventSubscriber/RouteSubscriber.php
RouteSubscriber.php in core/modules/field_ui/src/Routing/RouteSubscriber.php
RouteSubscriber.php in core/modules/block_content/src/Routing/RouteSubscriber.php
RouteSubscriber.php in core/modules/node/src/Routing/RouteSubscriber.php
RouteSubscriber.php in core/modules/media_library/src/Routing/RouteSubscriber.php
RouteSubscriber.php in core/modules/config_translation/src/Routing/RouteSubscriber.php
RouteSubscriber.php in core/modules/media/tests/modules/media_test_embed/src/Routing/RouteSubscriber.php
RouteTestSubscriber.php in core/modules/system/tests/modules/router_test_directory/src/RouteTestSubscriber.php
SpecialAttributesRouteSubscriber.php in core/lib/Drupal/Core/EventSubscriber/SpecialAttributesRouteSubscriber.php
UpdateRouteSubscriber.php in core/modules/update/src/Routing/UpdateRouteSubscriber.php

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