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

core/modules/migrate/src/MigrateMessageInterface.php

@@ -0,0 +1,21 @@
+<?php
+/**
+ * @file
+ * Contains \Drupal\migrate\MigrateMessageInterface.
+ */
+
+namespace Drupal\migrate;
+
+
+interface MigrateMessageInterface {
+
+  /**
+   * Displays a migrate message.
+   *
+   * @param string $message
+   *   The message to display.
+   * @param string $type
+   *   The type of message, for example: status or warning.
+   */
+  public function display($message, $type = 'status');
+}