/usr/share/php/Symfony/Component/Routing/Loader/ is in php-symfony-routing 3.4.6+dfsg-1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/php/Symfony/Component/Routing/Loader/AnnotationClassLoader.php
/usr/share/php/Symfony/Component/Routing/Loader/AnnotationDirectoryLoader.php
/usr/share/php/Symfony/Component/Routing/Loader/AnnotationFileLoader.php
/usr/share/php/Symfony/Component/Routing/Loader/ClosureLoader.php
/usr/share/php/Symfony/Component/Routing/Loader/Configurator/
/usr/share/php/Symfony/Component/Routing/Loader/Configurator/CollectionConfigurator.php
/usr/share/php/Symfony/Component/Routing/Loader/Configurator/ImportConfigurator.php
/usr/share/php/Symfony/Component/Routing/Loader/Configurator/RouteConfigurator.php
/usr/share/php/Symfony/Component/Routing/Loader/Configurator/RoutingConfigurator.php
/usr/share/php/Symfony/Component/Routing/Loader/Configurator/Traits/
/usr/share/php/Symfony/Component/Routing/Loader/Configurator/Traits/AddTrait.php
/usr/share/php/Symfony/Component/Routing/Loader/Configurator/Traits/RouteTrait.php
/usr/share/php/Symfony/Component/Routing/Loader/DependencyInjection/
/usr/share/php/Symfony/Component/Routing/Loader/DependencyInjection/ServiceRouterLoader.php
/usr/share/php/Symfony/Component/Routing/Loader/DirectoryLoader.php
/usr/share/php/Symfony/Component/Routing/Loader/GlobFileLoader.php
/usr/share/php/Symfony/Component/Routing/Loader/ObjectRouteLoader.php
/usr/share/php/Symfony/Component/Routing/Loader/PhpFileLoader.php
/usr/share/php/Symfony/Component/Routing/Loader/XmlFileLoader.php
/usr/share/php/Symfony/Component/Routing/Loader/YamlFileLoader.php
/usr/share/php/Symfony/Component/Routing/Loader/schema/
/usr/share/php/Symfony/Component/Routing/Loader/schema/routing/
/usr/share/php/Symfony/Component/Routing/Loader/schema/routing/routing-1.0.xsd