Chrome Version: 64.0.3269.3 (Official Build) dev (64-bit)
OS: All low-DPI devices

What steps will reproduce the problem?
(1) Visit https://stripe.com/docs/api#errors in Chrome
(2) Scroll the page

What is the expected result?

Nice smooth scrolling.

What happens instead?

Horrible janky scrolling.



So I see two things wrong here:

1. We aren't compositing the scrolling contents, likely because we can't determine the background color (and so aren't willing to lose LCD text). Stripe has a very weird way of doing the background; they style a sibling div to the content with a black background on the RHS, and use z-index to make sure its behind their (transparent) content div.

2. Our repainting is *very* slow. Firefox Nightly also repaints this page, but does it in a fraction of the time. Attached is a trace of me scrolling the page on Chrome 64; LocalFrameView::prePaint takes 88ms!


We should first confirm why we can't composite, and see if we can fix that. Failing that we should see if we can fix the high paint times.