fast/images/animated-webp.html [ ImageOnlyFailure Pass ] Quite frequently the test fails on the first run. This happened for the first time on r244375 (which is not related to the problem), but some revisions before there's r244372 which could be related. These are the images when it fails: https://build.webkit.org/results/GTK%20Linux%2064-bit%20Release%20(Tests)/r244868%20(10368)/fast/images/animated-webp-diffs.html
I'm going to close this as a duplicate of https://bugs.webkit.org/show_bug.cgi?id=197251 as seems to be the same issue. *** This bug has been marked as a duplicate of bug 197251 ***