12 files declare their use of RouteObjectInterface

AccessSubscriber.php in drupal/core/lib/Drupal/Core/EventSubscriber/AccessSubscriber.php
Contains Drupal\Core\EventSubscriber\AccessSubscriber.
FieldByClassEnhancer.php in drupal/core/vendor/symfony-cmf/routing/Symfony/Cmf/Component/Routing/Enhancer/FieldByClassEnhancer.php
HttpKernel.php in drupal/core/lib/Drupal/Core/HttpKernel.php
Definition of Drupal\Core\HttpKernel.
ParamConverterManager.php in drupal/core/lib/Drupal/Core/ParamConverter/ParamConverterManager.php
Contains Drupal\Core\ParamConverter\ParamConverterManager.
ProviderBasedGeneratorTest.php in drupal/core/vendor/symfony-cmf/routing/Symfony/Cmf/Component/Routing/Tests/Routing/ProviderBasedGeneratorTest.php
RequestHandler.php in drupal/core/modules/rest/lib/Drupal/rest/RequestHandler.php
Definition of Drupal\rest\RequestHandler.
RouteContentEnhancer.php in drupal/core/vendor/symfony-cmf/routing/Symfony/Cmf/Component/Routing/Enhancer/RouteContentEnhancer.php
RouteContentEnhancerTest.php in drupal/core/vendor/symfony-cmf/routing/Symfony/Cmf/Component/Routing/Tests/Enhancer/RouteContentEnhancerTest.php
RouteMock.php in drupal/core/vendor/symfony-cmf/routing/Symfony/Cmf/Component/Routing/Tests/Routing/RouteMock.php
RouteObject.php in drupal/core/vendor/symfony-cmf/routing/Symfony/Cmf/Component/Routing/Tests/Enhancer/RouteObject.php
UrlMatcher.php in drupal/core/vendor/symfony-cmf/routing/Symfony/Cmf/Component/Routing/NestedMatcher/UrlMatcher.php
UrlMatcherTest.php in drupal/core/vendor/symfony-cmf/routing/Symfony/Cmf/Component/Routing/Tests/NestedMatcher/UrlMatcherTest.php