That's just a testing artifact. Should be easy to fix by removing dumpChildFramesAsText.
Expected failing results committed in http://trac.webkit.org/changeset/77718.
I can't try removing dumpChildFramesAsText at the moment, but I will try later. Why is this only an issue on Windows?
Committed r77722: <http://trac.webkit.org/changeset/77722>
Oh noes! I think I just fixed it... We should revert the baseline...
http://trac.webkit.org/changeset/77722 might have broken GTK Linux 64-bit Debug