7 files declare their use of ReplaceCommand

ajax.inc in drupal/core/modules/views/includes/ajax.inc
Handles the server side AJAX interactions of Views.
AjaxCommandsUnitTest.php in drupal/core/modules/system/lib/Drupal/system/Tests/Ajax/AjaxCommandsUnitTest.php
Definition of Drupal\system\Tests\Ajax\AjaxCommandsUnitTest.
file.module in drupal/core/modules/file/file.module
Defines a "managed_file" Form API field and a "file" field for Field module.
system.admin.inc in drupal/core/modules/system/system.admin.inc
Admin page callbacks for the system module.
ViewEditFormController.php in drupal/core/modules/views_ui/lib/Drupal/views_ui/ViewEditFormController.php
Contains Drupal\views_ui\ViewEditFormController.
ViewsUIController.php in drupal/core/modules/views_ui/lib/Drupal/views_ui/Controller/ViewsUIController.php
Contains \Drupal\views_ui\Controller\ViewsUIController.
views_ui.module in drupal/core/modules/views_ui/views_ui.module
Provide structure for the administrative interface to Views.