Reftests take screenshot too early in Edge

[gsnedders]

Similar to #5412. w3c/csswg-drafts#1088 is the issue that causes issues here. Notably, wptrunner needs to:

• Block screenshots on fonts loading. (Unclear we can do this through JS or through WebDriver in any way given Edge doesn't support the Font Loading API.)
• Block screenshots on background images, list item images, etc. loading. (Unclear we can do this through JS or WebDriver in any way.)

Both of these are really problems web developers would hit if they wanted to do any screenshot-based testing over WebDriver, so I'd hope there's some way to work around them!

cc/ @patrickkettner @thejohnjansen

[thejohnjansen]

I am looking at the best solution that isn't just a hack for this. Internally we have a function that we call that tells us it's likely OK to take a screenshot. That is currently internal, though. I'm investigating making it external vs. possibly finding a better way. Currently the solutions I've found are all hacky, and we should avoid being hacky when it comes to stability jobs if possible.

[jgraham]

Can't WebDriver wait on that to take a screenshot? I'm happy to lobby for a spec change to make it official that you are exepcted to wait for a stable state after load before taking a screenshot. Otherwise we should add another load strategy to WebDriver for this purpose.

[gsnedders]

@jgraham See w3c/webdriver#893 wrt that.

[bobholt]

Looks like @gsnedders fixed the font issue for wpt, but the other still pending resolution of w3c/webdriver#893

[gsnedders]

@bobholt Uh, that commit message seems totally wrong. That commit shouldn't have changed anything in Edge, given Edge doesn't support the Font Loading API (currently "Under Consideration" on the Edge platform status page).

[foolip]

@thejohnjansen, do you have any update on #6327 (comment), something we could use both for the Travis CI runs and for wpt.fyi?

And does anyone know how widespread this issue? https://wpt.fyi/css/css-overflow/input-scrollable-region-001.html is one reftests that's passing in Edge and it's easy to find more, so at least not all reftests are failing.

[foolip]

This is about EdgeHTML, so should we close this issue? I'm guessing nobody will even run WPT against Edge 18 again...

[thejohnjansen]

I think it's fine to close this one out.