... more info to follow
If the assertion in RenderObject::locateFlowThreadContainingBlock is enabled for multicol, it fails on 6 tests: http://build.webkit.org/results/Apple%20Mavericks%20Debug%20WK2%20(Tests)/r168837%20(4654)/results.html
See https://bugs.webkit.org/show_bug.cgi?id=132906
This code has been significantly refactored since this patch was proposed. There doesn't seem to be any action we can take here.