[whatwg] sandboxed iframe allow-auto-play

Hello,

Recently I was talking with a web developer who told me one of his biggest
problems is dealing with "bad ads" that play audio/video immediately.

I was wondering if we could address this use case with some changes like:

1) Change sandboxed iframes to disable audio/video playing without user
interaction by default.
2) Add a new sandbox token "allow-auto-play" that permits playing without
user interaction.

Ideally this would effect flash running in the iframe as well, but its
unclear to me how feasible that is.  Still, this might be a nice step
towards improving this use case even without flash support.

Thoughts?

Thanks.

Ben