Issue #2201785 by sun, Berdir: Remove drupal_flush_all_caches() from installer.

core/includes/install.core.inc

@@ -1512,7 +1512,6 @@ function install_profile_modules(&$install_state) {
     'operations' => $operations,
     'title' => t('Installing @drupal', array('@drupal' => drupal_install_profile_distribution_name())),
     'error_message' => t('The installation has encountered an error.'),
-    'finished' => '_install_profile_modules_finished',
   );
   return $batch;
 }
@@ -1690,10 +1689,10 @@ function install_finished(&$install_state) {
   // Installation profiles are always loaded last.
   module_set_weight($profile, 1000);
 
-  // Flush all caches to ensure that any full bootstraps during the installer
-  // do not leave stale cached data, and that any content types or other items
-  // registered by the installation profile are registered correctly.
-  drupal_flush_all_caches();
+  // Build the router once after installing all modules.
+  // This would normally happen upon KernelEvents::TERMINATE, but since the
+  // installer does not use an HttpKernel, that event is never triggered.
+  \Drupal::service('router.builder')->rebuild();
 
   // Run cron to populate update status tables (if available) so that users
   // will be warned if they've installed an out of date Drupal version.
@@ -1733,15 +1732,6 @@ function _install_module_batch($module, $module_name, &$context) {
   $context['message'] = t('Installed %module module.', array('%module' => $module_name));
 }
 
-/**
- * 'Finished' callback for module installation batch.
- */
-function _install_profile_modules_finished($success, $results, $operations) {
-  // Flush all caches to complete the module installation process. Subsequent
-  // installation tasks will now have full access to the profile's modules.
-  drupal_flush_all_caches();
-}
-
 /**
  * Checks installation requirements and reports any errors.
  */