Since the last show/hide call should be effective, implement it without requiring an extra interface property. https://bugzilla.gnome.org/show_bug.cgi?id=762083
This is an interface that can be used to implement the "application is not responding" dialog. One instance is created per window, which is initially hidden, and can be shown/hidden on demand. https://bugzilla.gnome.org/show_bug.cgi?id=711619