constructing new VideoFrame(HTMLVideoElement,...) shouldn't rely on <video>.networkState

[chcunningham]

Right now the constructor's steps say

If image’s networkState attribute is NETWORK_EMPTY, then throw an InvalidStateError DOMException.

This was a copy paste from createImageBitmap() steps.

But networkState really doesn't have any correspondence to "is your video element ready to render a frame".

There's a related discussion in Chrome's bug tracker where play() promise resolution (and thereby readyState > HAVE_CURRENT_DATA) is proposed as the signal that a frame is ready. Some unanswered questions there, and maybe some risk to making that change.

[chcunningham]

This test demonstrates the issue https://chromium-review.googlesource.com/c/chromium/src/+/3612133