fast/encoding/utf-16-big-endian.html and fast/encoding/utf-16-little-endian.html just failed for the first time with small text size differences: https://build.webkit.org/builders/Apple%20Yosemite%20Release%20WK2%20(Tests)/builds/1599 Looks like they became flaky after enabling kerning. Perhaps running the tests in the same order as in this run will make this reproducible.
http://trac.webkit.org/changeset/178573 fixed it.