In GTK+ 3, it's mandatory to have a GdkDevice in a synthesized event,
so fill in the pointer device for the events we synthesize and forward
to GTK+. Since gdk_event_set_device() only works for allocated events,
we need to switch to gdk_event_new() rather than using stack allocated
events.
https://bugzilla.gnome.org/show_bug.cgi?id=633401