New experimental API is added to allow changing the way that redraws
are timed for a stage to include a "sync delay" - a period after
the vertical blanking period where Clutter simply waits for updates.
In detail, the algorithm is that when the master clock is restarted
after drawing a frame (in the case where there are timelines running)
or started fresh in response to a queued redraw or relayout, the
start is scheduled at the next sync point (sync_delay ms after the
predicted vblank period) rather than done immediately.
https://bugzilla.gnome.org/show_bug.cgi?id=692901
b248941af5