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

core/modules/field/src/FieldConfigInterface.php

@@ -0,0 +1,26 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\field\FieldConfigInterface.
+ */
+
+namespace Drupal\field;
+
+use Drupal\Core\Config\Entity\ConfigEntityInterface;
+use Drupal\Core\Field\FieldDefinitionInterface;
+
+/**
+ * Provides an interface defining a field entity.
+ */
+interface FieldConfigInterface extends ConfigEntityInterface, FieldDefinitionInterface {
+
+  /**
+   * Gets the deleted flag of the field.
+   *
+   * @return bool
+   *   Returns TRUE if the field is deleted.
+   */
+  public function isDeleted();
+
+}