We add an entire class like we do for parsing other codec initialization formats; it's currently not doing any parsing though (... initialization data is really simple for AV1 though: just the entire contents of the box).
For testing, we add the sample file, having been re-encoded with ffmpeg (and we also happen to have another av1 file, too).
PiperOrigin-RevId: 444890282
a16c0b3068