13 files declare their use of Route

AdminController.php in core/modules/system/src/Controller/AdminController.php
AttributeRouteDiscoveryTest.php in core/tests/Drupal/Tests/Core/Routing/AttributeRouteDiscoveryTest.php
BlockContentController.php in core/modules/block_content/src/Controller/BlockContentController.php
Http4xxController.php in core/modules/system/src/Controller/Http4xxController.php
PerformanceController.php in core/modules/system/src/Controller/PerformanceController.php
SiteInformationForm.php in core/modules/system/src/Form/SiteInformationForm.php
SystemController.php in core/modules/system/src/Controller/SystemController.php
SystemInfoController.php in core/modules/system/src/Controller/SystemInfoController.php
TestAttributes.php in core/modules/system/tests/modules/router_test_directory/src/Controller/TestAttributes.php
ThemeController.php in core/modules/system/src/Controller/ThemeController.php
TitleClosureTest.php in core/tests/Drupal/KernelTests/Core/Routing/TitleClosureTest.php
TitleResolver.php in core/lib/Drupal/Core/Controller/TitleResolver.php
TitleResolverTest.php in core/tests/Drupal/Tests/Core/Controller/TitleResolverTest.php

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