Make high resolution time dependant on cross-origin isolated

[annevk]

With #88 solved, it would be good if the 5 microseconds resolution would be made conditional upon cross-origin isolated.

See whatwg/html#4734. Though see whatwg/html#5435 about potentially having to refer a slightly different concept.

[yoavweiss]

/cc @mikewest

[mikewest]

This sounds pretty reasonable to me.

[yoavweiss]

Should this be blocked on the definition of isolated contexts?

[npm1]

Chrome's current resolution is 5 microseconds for platforms other than Android. Does that mean we'll need to coarsen the timer more for these platforms? What would be the new maximum resolution for non-isolated?

[yoavweiss]

This was discussed at a WebPerfWG call a couple of months back.

It was decided that once the underlying primitives are integrated into HTML (which I believe they now are), we'd estimate if this goes into L2 or L3 based on the changes themselves.

[npm1]

Is cross-origin isolated now shipped in browsers? What's the next step here?

[yoavweiss]

I think the next step is for me to try and take a stab as defining something that outlines what browsers are currently doing, and what COEP/COOP would enable them to do.