[gnome-shell] panel: Keep prefs in sync with shell-shows-app-menu state

[Florian Müllner <fmuellner src gnome org>]

commit 900398406c894f000fb59cbc4f7b1214eacb457d
Author: Jonas Ådahl <jadahl gmail com>
Date:   Thu Aug 23 15:56:50 2018 +0200

    panel: Keep prefs in sync with shell-shows-app-menu state
    
    Previously mutter listened to Xsettings (via GTK) to get notified
    whether the shell showed the app menu. After X11 support was changed in
    the direction of being less central, listening to this particular
    Xsettings were removed with the intention of having the Shell tell
    mutter directly whether it was showing the menu or not.
    
    This commit makes that happen. It still travels through Xsettings (still
    via Gtk), as the shell still gets that state from Xsettings, but fixing
    this is out of scope for this particular fix.
    
    Closes: https://gitlab.gnome.org/GNOME/mutter/issues/276

 js/ui/panel.js | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
---
diff --git a/js/ui/panel.js b/js/ui/panel.js
index 4fd599c47..3726b8445 100644
--- a/js/ui/panel.js
+++ b/js/ui/panel.js
@@ -307,8 +307,11 @@ var AppMenuButton = new Lang.Class({
             }
         }
 
+        let shellShowsAppMenu = this._gtkSettings.gtk_shell_shows_app_menu;
+        Meta.prefs_set_show_fallback_app_menu(!shellShowsAppMenu);
+
         let visible = (this._targetApp != null &&
-                       this._gtkSettings.gtk_shell_shows_app_menu &&
+                       shellShowsAppMenu &&
                        !Main.overview.visibleTarget);
         if (visible)
             this.show();