Created attachment 201125 [details]
There should be a box shadow on the parent of the gray box in the testcase, but it's missing.
Regressed at http://trac.webkit.org/changeset/145680
Ah, there's a code path where paintFillLayer() paints the box shadow.
…which was done to fix bug 78728.
Created attachment 201134 [details]
Created attachment 201136 [details]
The simpler approach might be better. I'm not sure if it is semantically correct to consider box shadow in background extent.
Comment on attachment 201136 [details]
View in context: https://bugs.webkit.org/attachment.cgi?id=201136&action=review
> + LayoutRect backgroundRect = pixelSnappedIntRect(style()->boxShadow() ? boxShadowExtent() : borderBoxRect());
I think it's confusing for a function called backgroundPaintedExtent() to return the box shadow extent, unless you rename it to boxDecorationExtent().
This patch also means that you'll always consult box shadows for obscuration, even when the background might be obscured and the shadow drawn separately. So I prefer my patch.