The test fast/forms/auto-fill-button/input-readonly-auto-fill-button.html fails on platform GTK since it was added on r185166 <http://trac.webkit.org/r185166> The diff is the following: https://build.webkit.org/results/GTK%20Linux%2064-bit%20Release%20%28Tests%29/r185166%20%289031%29/fast/forms/auto-fill-button/input-readonly-auto-fill-button-diffs.html
I think this was fixed by r187095. Unskipped in r191101.