On platform GTK the following tests are flaky:
fast/multicol/scrolling-overflow.html [ Failure Pass ]
fast/multicol/span/span-as-immediate-child-generated-content.html [ Failure Pass ]
The results for this two tests were rebaselined on r168097 <http://trac.webkit.org/changeset/168097> after the new multi-column mode was enabled.
However, after the rebaseline, this two tests now are flaky. So I also marked them as such on r168097.
So perhaps there is something wrong with the new multi-column mode on GTK that causes this.