visual regression visualDiff hangs forever when tab is in background

[melink14]

With new headless chrome (and headfull), if the tab is in the background takeScreenshot never returns (and no timeouts fire until the top level 120s timer fires;)

This is because element.screenshot in puppeteer relies on IntersectionObserver (via scrollIntoViewIfAble) doesn't work in backgrounded tabs. (ref: https://github.com/puppeteer/puppeteer/blob/682bb682116437dc803afd613eb95fd2efd65a65/packages/puppeteer-core/src/api/ElementHandle.ts#L1479)

I made a local patch where I just added page.bringToFront() before calling element.screenshot and that seems to work though I'm not sure if there's a better fix. (ref:

web/packages/test-runner-visual-regression/src/visualRegressionPlugin.ts

Line 79 in 17cfc0d

const screenshot = await element.screenshot({ encoding: 'binary' });

)

It seems like when the simlar #2366 was merged it added a __bringTabToFront method to window which I could call before visualDiff as well but it seems like an implementation detail I shouldn't rely on.

For now, I can use patch-package but I'd love to hear thoughts on this approach.

For completeness, similar to other new headless bugs, this can be fixed by setting concurrency to 1 as well.

(As an aside, given we patched requestAnimationFrame I wonder if we should also patch client side IntersectionObserver to call bringTabToFront...)

[melink14]

(A similar problem for .click was opened on puppeteer: puppeteer/puppeteer#5201)