8 files declare their use of HtmlCommand in Zircon Profile 8.0

AjaxCommandsTest.php in core/tests/Drupal/Tests/Core/Ajax/AjaxCommandsTest.php

Contains \Drupal\Tests\Core\Ajax\AjaxCommandsTest.

AjaxTestController.php in core/modules/system/tests/modules/ajax_test/src/Controller/AjaxTestController.php

Contains \Drupal\ajax_test\Controller\AjaxTestController.

Callbacks.php in core/modules/system/tests/modules/ajax_forms_test/src/Callbacks.php

Contains \Drupal\ajax_forms_test\Callbacks.

CommandsTest.php in core/modules/system/src/Tests/Ajax/CommandsTest.php

Contains \Drupal\system\Tests\Ajax\CommandsTest.

EditorImageDialog.php in core/modules/editor/src/Form/EditorImageDialog.php

Contains \Drupal\editor\Form\EditorImageDialog.

EditorLinkDialog.php in core/modules/editor/src/Form/EditorLinkDialog.php

Contains \Drupal\editor\Form\EditorLinkDialog.

FrameworkTest.php in core/modules/system/src/Tests/Ajax/FrameworkTest.php

Contains \Drupal\system\Tests\Ajax\FrameworkTest.

ViewEditForm.php in core/modules/views_ui/src/ViewEditForm.php

Contains \Drupal\views_ui\ViewEditForm.