svg/filters/sourceAlpha-input-filter-effect.html is failing on Windows. <https://build.webkit.org/results/Apple%20Win%207%20Release%20(Tests)/r183568%20(51454)/results.html>
Test expectation added in r183637.
This appears to have started working around r190616-r190619.
I think the fixes for composited/layered drawing scaling and offset calculations fixed this bug. Fixed by <https://trac.webkit.org/browser/?rev=190616> (as well as the related changes leading up to that final fix).