The following layout test is failing on GTK+ since it was added on r181292 (http://trac.webkit.org/changeset/181292). The difference is very tiny and its difficult to appreciate it: https://build.webkit.org/results/GTK%20Linux%2064-bit%20Release%20%28Tests%29/r181690%20%287039%29/fast/text/baseline-inline-block-diffs.html
This was failing due to the Ahem font beeing antialiased (which it shouldn't). In this specific case, the author of the test even tried to force anti-aliasing off via the CSS property "-webkit-font-smoothing: none;" but we weren't supporting it.
There are no references to this bug in any TestExpectations. It's probable this bug was solved at some point but it wasn't marked as closed. I'm closing this bug now. If you think this bug report is still valid, please reopen it and add an entry to TestExpectations.
<rdar://problem/104678766>