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

core/modules/taxonomy/src/VocabularyStorageInterface.php

@@ -0,0 +1,28 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\taxonomy\VocabularyStorageInterface.
+ */
+
+namespace Drupal\taxonomy;
+
+use Drupal\Core\Config\Entity\ConfigEntityStorageInterface;
+
+/**
+ * Defines an interface for vocabulary entity storage classes.
+ */
+interface VocabularyStorageInterface extends ConfigEntityStorageInterface {
+
+  /**
+   * Gets top-level term IDs of vocabularies.
+   *
+   * @param array $vids
+   *   Array of vocabulary IDs.
+   *
+   * @return array
+   *   Array of top-level term IDs.
+   */
+  public function getToplevelTids($vids);
+
+}