Add hb_buffer_serialize_list_formats()
diff --git a/src/hb-buffer.h b/src/hb-buffer.h
index ba9cd1d..db9b40f 100644
--- a/src/hb-buffer.h
+++ b/src/hb-buffer.h
@@ -259,6 +259,9 @@
 const char *
 hb_buffer_serialize_format_to_string (hb_buffer_serialize_format_t format);
 
+const char **
+hb_buffer_serialize_list_formats (void);
+
 /* Returns number of items, starting at start, that were serialized. */
 unsigned int
 hb_buffer_serialize_glyphs (hb_buffer_t *buffer,