19 files declare their use of RedirectResponse

AggregatorController.php in drupal/core/modules/aggregator/lib/Drupal/aggregator/Controller/AggregatorController.php
Contains \Drupal\aggregator\Controller\AggregatorController.
common.inc in drupal/core/includes/common.inc
Common functions that many Drupal modules will need to reference.
ConfigTestController.php in drupal/core/modules/config/tests/config_test/lib/Drupal/config_test/ConfigTestController.php
Contains \Drupal\config_test\ConfigTestController.
config_test.module in drupal/core/modules/config/tests/config_test/config_test.module
Provides Config module hook implementations for testing purposes.
CronController.php in drupal/core/modules/system/lib/Drupal/system/CronController.php
Definition of Drupal\system\CronController.
CronForm.php in drupal/core/modules/system/lib/Drupal/system/Form/CronForm.php
Contains \Drupal\system\Form\CronForm.
custom_block.pages.inc in drupal/core/modules/block/custom_block/custom_block.pages.inc
Provides page callbacks for custom blocks.
HttpKernelTest.php in drupal/core/vendor/symfony/http-kernel/Symfony/Component/HttpKernel/Tests/HttpKernelTest.php
install.inc in drupal/core/includes/install.inc
API functions for installing modules and themes.
MaintenanceModeSubscriber.php in drupal/core/lib/Drupal/Core/EventSubscriber/MaintenanceModeSubscriber.php
Contains \Drupal\Core\EventSubscriber\MaintenanceModeSubscriber.
MaintenanceModeSubscriber.php in drupal/core/modules/user/lib/Drupal/user/EventSubscriber/MaintenanceModeSubscriber.php
Contains \Drupal\user\EventSubscriber\MaintenanceModeSubscriber.
OverlaySubscriber.php in drupal/core/modules/overlay/lib/Drupal/overlay/EventSubscriber/OverlaySubscriber.php
Contains \Drupal\overlay\EventSubscriber\OverlaySubscriber.
RedirectResponseTest.php in drupal/core/vendor/symfony/http-foundation/Symfony/Component/HttpFoundation/Tests/RedirectResponseTest.php
RouterDataCollector.php in drupal/core/vendor/symfony/http-kernel/Symfony/Component/HttpKernel/DataCollector/RouterDataCollector.php
ThemeController.php in drupal/core/modules/system/lib/Drupal/system/Controller/ThemeController.php
Contains \Drupal\system\Controller\ThemeController.
user.pages.inc in drupal/core/modules/user/user.pages.inc
User page callback file for the user module.
UserController.php in drupal/core/modules/user/lib/Drupal/user/Controller/UserController.php
Contains \Drupal\user\Controller\UserController.
ViewsFormBase.php in drupal/core/modules/views_ui/lib/Drupal/views_ui/Form/Ajax/ViewsFormBase.php
Contains \Drupal\views_ui\Form\Ajax\ViewsFormBase.
ViewsUIController.php in drupal/core/modules/views_ui/lib/Drupal/views_ui/Controller/ViewsUIController.php
Contains \Drupal\views_ui\Controller\ViewsUIController.