Index: src/wp-admin/includes/post.php
===================================================================
--- src/wp-admin/includes/post.php	(revision 29907)
+++ src/wp-admin/includes/post.php	(working copy)
@@ -1529,6 +1529,8 @@
 		$new_autosave['ID'] = $old_autosave->ID;
 		$new_autosave['post_author'] = $post_author;

+		do_action( '_wp_creating_autosave', $new_autosave );
+
 		// If the new autosave has the same content as the post, delete the autosave.
 		$post = get_post( $post_id );
 		$autosave_is_different = false;