This is needed to make sure that client-side and server-side
decorations have same button layout.

GNOME Settings Daemon will update Gtk/DecorationLayout from
button-layout. At this point everything should be ok.

But then it is possible to override Gtk/DecorationLayout from
xsettings plugin in GNOME Settings Daemon. At this point we can
end up with different button layouts between client-side and
server-side decorations. I can not think any reason why someone
would want different button layouts.