The following layout test is flaky on platform GTK fast/regions/repaint/fixed-in-named-flow-cb-changed2.html When it fails, gives this result: http://build.webkit.org/results/GTK%20Linux%2064-bit%20Release%20%28Tests%29/r171262%20%281539%29/fast/regions/repaint/fixed-in-named-flow-cb-changed2-diffs.html
CSS Regions were removed in Bug 174978.