[gnome-shell] extensionSystem: add missing import

[Owen Taylor <otaylor src gnome org>]

commit b7513097eaf72725086767ad7f467ddab592738a
Author: Maxim Ermilov <zaspire rambler ru>
Date:   Tue Apr 5 05:20:44 2011 +0400

    extensionSystem: add missing import
    
    https://bugzilla.gnome.org/show_bug.cgi?id=646333

 js/ui/extensionSystem.js |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/js/ui/extensionSystem.js b/js/ui/extensionSystem.js
index eb82bc3..9dd3a47 100644
--- a/js/ui/extensionSystem.js
+++ b/js/ui/extensionSystem.js
@@ -3,6 +3,7 @@
 const GLib = imports.gi.GLib;
 const Gio = imports.gi.Gio;
 const St = imports.gi.St;
+const Shell = imports.gi.Shell;
 
 const Config = imports.misc.config;