Like in the case of gaps (bug #156288), positioned items are not working properly with content alignment. This has been fixed in Blink already: https://codereview.chromium.org/1870623002/
Created attachment 276423 [details] Patch The patch has been developed on top of patch for bug #156589 (so it doesn't apply in trunk).
Created attachment 276424 [details] Patch
Comment on attachment 276424 [details] Patch Annoying to have these tests that just write out PASS PASS PASS. Would be nicer some day to use reference tests or to pave the tests write something more about what they are testing so if something fails you can get a better understanding of what.
Comment on attachment 276424 [details] Patch Thanks for the review. The problem with reference tests is the 800x600 viewport size, we would need a lot of different tests to check all the cases or use smaller sizes for everything so it'd be harder to debug. I agree that the tests full of PASS are not very nice, but when they fail they provide quite a lot of information.
Comment on attachment 276424 [details] Patch Clearing flags on attachment: 276424 Committed r199657: <http://trac.webkit.org/changeset/199657>
All reviewed patches have been landed. Closing bug.