window.scrollX should agree with document.body.scrollLeft
Created attachment 107337 [details] Patch
This test case shows how window.scrollX differs from document.body.scrollLeft (and similarly window.scrollY with document.body.scrollTop) when the page is scaled with EventSender.scalePageBy. Please let me know if you agree or not with this test case.
Comment on attachment 107337 [details] Patch We can't land a page without a source change that fixes the bug.