The fast/regions/overflow/overflow-region-float.html layout test is failing on GTK since r177658 (trac.webkit.org/changeset/177658). This test changes dashed and dotted border painting and it causes that one part of border of the test is not rendered. The diff is the following: https://build.webkit.org/results/GTK%20Linux%2064-bit%20Release%20%28Tests%29/r181476%20%286927%29/fast/regions/overflow/overflow-region-float-diffs.html
This has been passing since r191658. Committed r194306: <http://trac.webkit.org/changeset/194306>