The css3/masking/mask-svg-no-fragmentId.html layout test is flaky on GTK. Ocasionally, it fails. When it fails the diff is the following: https://build.webkit.org/results/GTK%20Linux%2064-bit%20Release%20%28Tests%29/r183043%20%287839%29/css3/masking/mask-svg-no-fragmentId-diffs.html It seems to be related with the rendering of the P letter from "specifying".
The css3/masking/mask-svg-invalid-fragmentId.html is also flaky on GTK+. The diff is the following: https://build.webkit.org/results/GTK%20Linux%2064-bit%20Release%20%28Tests%29/r184558%20%288672%29/css3/masking/mask-svg-invalid-fragmentId-diffs.html
r177494 was reverted on r186391 And this test removed