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

core/modules/file/src/FileUsage/FileUsageBase.php

@@ -0,0 +1,40 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\file\FileUsage\FileUsageBase.
+ */
+
+namespace Drupal\file\FileUsage;
+
+use Drupal\file\FileInterface;
+
+/**
+ * Defines the base class for database file usage backend.
+ */
+abstract class FileUsageBase implements FileUsageInterface {
+
+  /**
+   * Implements Drupal\file\FileUsage\FileUsageInterface::add().
+   */
+  public function add(FileInterface $file, $module, $type, $id, $count = 1) {
+    // Make sure that a used file is permanent.
+    if (!$file->isPermanent()) {
+      $file->setPermanent();
+      $file->save();
+    }
+  }
+
+  /**
+   * Implements Drupal\file\FileUsage\FileUsageInterface::delete().
+   */
+  public function delete(FileInterface $file, $module, $type = NULL, $id = NULL, $count = 1) {
+    // If there are no more remaining usages of this file, mark it as temporary,
+    // which result in a delete through system_cron().
+    $usage = \Drupal::service('file.usage')->listUsage($file);
+    if (empty($usage)) {
+      $file->setTemporary();
+      $file->save();
+    }
+  }
+}