The extra reference will be held from GdkEventPrivate data, so there's
a common place to all events. Without this, events queued after devices/
capabilities disappear (eg. on TTY switch) might hold invalid pointers.
Windowing level operations on those devices (queries, grabs...) are
expected to fail at that time, but we should hold meaningful data for
the regular event handling paths.

https://bugzilla.gnome.org/show_bug.cgi?id=753185