Action names sometimes unintentionally overlap with icon names, so
we should only create icon buttons if the message tray source requests
it. For the notification daemon, this is done by setting the
'action-icons' hint on the notification.
The previous notification server capability used to advertise this
feature, "x-gnome-icon-buttons", has been removed in favour of the
new capability described in the notification spec, "action-icons".
https://bugzilla.gnome.org/show_bug.cgi?id=624584
9585c823d5