Index: src/wp-includes/ms-files.php
===================================================================
--- src/wp-includes/ms-files.php	(revision 28998)
+++ src/wp-includes/ms-files.php	(working copy)
@@ -16,6 +16,13 @@
 
 ms_file_constants();
 
+/**
+ * Fires before file loading process for Multisite medias starts.
+ *
+ * @since 
+ */
+do_action( 'ms_load_files' );
+
 error_reporting( 0 );
 
 if ( $current_blog->archived == '1' || $current_blog->spam == '1' || $current_blog->deleted == '1' ) {