Drupal 8.0.0 beta 12. More info: https://www.drupal.org/node/2514176

core/modules/user/src/RoleAccessControlHandler.php

@@ -0,0 +1,37 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\user\RoleAccessControlHandler.
+ */
+
+namespace Drupal\user;
+
+use Drupal\Core\Access\AccessResult;
+use Drupal\Core\Entity\EntityAccessControlHandler;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Session\AccountInterface;
+
+/**
+ * Defines the access control handler for the user role entity type.
+ *
+ * @see \Drupal\user\Entity\Role
+ */
+class RoleAccessControlHandler extends EntityAccessControlHandler {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function checkAccess(EntityInterface $entity, $operation, $langcode, AccountInterface $account) {
+    switch ($operation) {
+      case 'delete':
+        if ($entity->id() == RoleInterface::ANONYMOUS_ID || $entity->id() == RoleInterface::AUTHENTICATED_ID) {
+          return AccessResult::forbidden();
+        }
+
+      default:
+        return parent::checkAccess($entity, $operation, $langcode, $account);
+    }
+  }
+
+}