It fails in the debug bots, skipping until we can check it. Probably it is
The error is this:
instance of invalid non-instantiatable type `(null)'
g_signal_emit_by_name: assertion `G_TYPE_CHECK_INSTANCE (instance)' failed
Check how bug 37537 and bug 37545 could be false positives of this one.
The test is consistently passing so its expectation was removed in http://trac.webkit.org/changeset/120476. Closing the bug.