Deprecate these APIs on HTMLVideoElement:
readonly attribute boolean webkitSupportsFullscreen;
readonly attribute boolean webkitDisplayingFullscreen;
// Note the different capitalization of the "S" in FullScreen.
Usage information from UseCounter
These numbers were provided to me by Adam Barth:
PrefixedVideoEnterFullScreen < 0.00001%
PrefixedVideoExitFullScreen < 0.00001%
These counters have, IIUC, just reached the stable channel, so another check will be needed before removal.
When removed, sites that use *only* this API with no fallback will simply stop supporting fullscreen. Given the usage counts this does not seem catastrophic, and it's likely that at least some of the current pages using this would fall back to another code path if the APIs were removed.
Row on feature dashboard?