7 calls to drupal_maintenance_theme() in Drupal 8
- authorize.php in core/
authorize.php  - Administrative script for running authorized file operations.
 - drupal_flush_all_caches in core/
includes/ common.inc  - Flushes all persistent caches, resets all variables, and rebuilds all data structures.
 - install_begin_request in core/
includes/ install.core.inc  - Begins an installation request, modifying the installation state as needed.
 - install_display_output in core/
includes/ install.core.inc  - Displays themed installer output and ends the page request.
 - install_run_tasks in core/
includes/ install.core.inc  - Runs all tasks for the current installation request.
 - MaintenanceModeSubscriber::onKernelRequestMaintenance in core/
lib/ Drupal/ Core/ EventSubscriber/ MaintenanceModeSubscriber.php  - Returns the site maintenance page if the site is offline.
 - MaintenanceThemeTest::testMaintenanceTheme in core/
tests/ Drupal/ KernelTests/ Core/ Theme/ MaintenanceThemeTest.php  - Tests that the maintenance theme initializes the theme and its base themes.