Store GjsContext pointer in ShellGlobal

Future functionality in ShellGlobal needs access to the GjsContext.

https://bugzilla.gnome.org/show_bug.cgi?id=599561

src/shell-global-private.h

@@ -0,0 +1,12 @@
+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
+#ifndef __SHELL_GLOBAL_PRIVATE_H__
+#define __SHELL_GLOBAL_PRIVATE_H__
+
+#include "shell-global.h"
+
+#include <gjs/gjs.h>
+
+void _shell_global_set_gjs_context (ShellGlobal *global,
+                                    GjsContext  *context);
+
+#endif /* __SHELL_GLOBAL_PRIVATE_H__ */