Lots of late frames reported with high playbackRate

[bvibber]

I'm seeing higher frame time delays and some dropped frames when going full-tilt on playbackRate as on https://brionv.com/misc/ogv.js/demo2/#file=STS-132_Liftoff_Space_Shuttle_Atlantis.ogv&size=240p.vp9.webm&source=motd with it cranked up, even though reported decode time looks fine.

I think the timers for frame-not-ready-to-play need to be updated to compensate for playbackRate? And the stats need to adjust for real time as well, so everything's more consistent.