This two layout test fail when you run them on a Retina Macbook Pro or any Mac running in HiDPI mode: fast/events/wheelevent-in-horizontal-scrollbar-in-rtl.html fast/events/wheelevent-in-vertical-scrollbar-in-rtl.html Here is the failure for one of them: --- /Volumes/Big/Build/symroots/Debug/layout-test-results/fast/events/wheelevent-in-vertical-scrollbar-in-rtl-expected.txt +++ /Volumes/Big/Build/symroots/Debug/layout-test-results/fast/events/wheelevent-in-vertical-scrollbar-in-rtl-actual.txt @@ -1,3 +1,3 @@ Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum." window.scrollX: 84 -window.scrollY: -108 +window.scrollY: -109 It seems likely that we are rounding or truncating at some point because of our integer-based layout system, and we're getting it wrong. It would be nice in the short term to have a new directory like the platform directory for test results that are specific to different deviceScaleFactors.