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

core/modules/field/src/FieldConfigAccessControlHandler.php

@@ -0,0 +1,38 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\field\FieldConfigAccessControlHandler.
+ */
+
+namespace Drupal\field;
+
+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 field entity type.
+ *
+ * @see \Drupal\field\Entity\FieldConfig
+ */
+class FieldConfigAccessControlHandler extends EntityAccessControlHandler {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function checkAccess(EntityInterface $entity, $operation, $langcode, AccountInterface $account) {
+    if ($operation == 'delete') {
+      $field_storage_entity = $entity->getFieldStorageDefinition();
+      if ($field_storage_entity->isLocked()) {
+        return AccessResult::forbidden()->cacheUntilEntityChanges($field_storage_entity);
+      }
+      else {
+        return AccessResult::allowedIfHasPermission($account, 'administer ' . $entity->getTargetEntityTypeId() . ' fields')->cacheUntilEntityChanges($field_storage_entity);
+      }
+    }
+    return AccessResult::allowedIfHasPermission($account, 'administer ' . $entity->getTargetEntityTypeId() . ' fields');
+  }
+
+}