22 files declare their use of JsonResponse

ajax.inc in drupal/core/modules/views/includes/ajax.inc
Handles the server side AJAX interactions of Views.
AjaxResponse.php in drupal/core/lib/Drupal/Core/Ajax/AjaxResponse.php
Definition of Drupal\Core\Ajax\AjaxResponse.
batch.inc in drupal/core/includes/batch.inc
Batch processing API for processes to run in multiple HTTP requests.
ContextualController.php in drupal/core/modules/contextual/lib/Drupal/contextual/ContextualController.php
Contains \Drupal\contextual\ContextualController.
database_test.module in drupal/core/modules/system/tests/modules/database_test/database_test.module
EditController.php in drupal/core/modules/edit/lib/Drupal/edit/EditController.php
Contains of \Drupal\edit\EditController.
EntityReferenceController.php in drupal/core/modules/entity_reference/lib/Drupal/entity_reference/EntityReferenceController.php
Contains \Drupal\entity_reference/EntityReferenceController.
ExceptionController.php in drupal/core/lib/Drupal/Core/Controller/ExceptionController.php
Contains \Drupal\Core\Controller\ExceptionController.
file.module in drupal/core/modules/file/file.module
Defines a "managed_file" Form API field and a "file" field for Field module.
form_test.module in drupal/core/modules/system/tests/modules/form_test/form_test.module
Helper module for the form API tests.
JsonResponseTest.php in drupal/core/vendor/symfony/http-foundation/Symfony/Component/HttpFoundation/Tests/JsonResponseTest.php
MachineNameController.php in drupal/core/modules/system/lib/Drupal/system/MachineNameController.php
Contains \Drupal\system\MachineNameController.
menu.module in drupal/core/modules/menu/menu.module
Allows administrators to customize the site's navigation menus.
system.admin.inc in drupal/core/modules/system/system.admin.inc
Admin page callbacks for the system module.
system.module in drupal/core/modules/system/system.module
Configuration system that lets administrators modify the workings of the site.
taxonomy.pages.inc in drupal/core/modules/taxonomy/taxonomy.pages.inc
Page callbacks for the taxonomy module.
toolbar.module in drupal/core/modules/toolbar/toolbar.module
Administration toolbar for quick access to top level administration items.
ToolbarController.php in drupal/core/modules/toolbar/lib/Drupal/toolbar/Routing/ToolbarController.php
Contains \Drupal\toolbar\Routing\ToolbarController.
user.pages.inc in drupal/core/modules/user/user.pages.inc
User page callback file for the user module.
UserAutocompleteController.php in drupal/core/modules/user/lib/Drupal/user/Controller/UserAutocompleteController.php
Contains \Drupal\user\Controller\UserAutocompleteController.
ViewSubscriber.php in drupal/core/lib/Drupal/Core/EventSubscriber/ViewSubscriber.php
Definition of Drupal\Core\EventSubscriber\ViewSubscriber.
ViewsUIController.php in drupal/core/modules/views_ui/lib/Drupal/views_ui/Controller/ViewsUIController.php
Contains \Drupal\views_ui\Controller\ViewsUIController.