6 files declare their use of RequestContext in Zircon Profile 8

PathBasedBreadcrumbBuilder.php in core/modules/system/src/PathBasedBreadcrumbBuilder.php

Contains \Drupal\system\PathBasedBreadcrumbBuilder.

PathFormBase.php in core/modules/path/src/Form/PathFormBase.php

Contains \Drupal\path\Form\PathFormBase.

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

Contains \Drupal\Core\EventSubscriber\RedirectResponseSubscriber.

SiteInformationForm.php in core/modules/system/src/Form/SiteInformationForm.php

Contains \Drupal\system\Form\SiteInformationForm.

TrustedRedirectResponseTest.php in core/tests/Drupal/Tests/Core/Routing/TrustedRedirectResponseTest.php

Contains \Drupal\Tests\Core\Routing\TrustedRedirectResponseTest.

UrlGeneratorTest.php in core/tests/Drupal/Tests/Core/Routing/UrlGeneratorTest.php

Contains \Drupal\Tests\Core\Routing\UrlGeneratorTest.