This is a `GSource` which is dispatched when the offset of the system
real/wall clock changes with respect to the system monotonic clock. This
can happen when the user explicitly changes the system clock, or when
there’s an NTP sync after a prolonged period offline.
The source can’t tell you *what* the offset change was, just that there
was one.
This will be used in an upcoming commit.
Signed-off-by: Philip Withnall <pwithnall@gnome.org>
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3397>
