I think that I've seen these tests fail somewhere before (maybe locally?), but today they started to fail 100% of time, and I think that this is because we now have up to date WebCore Web Inspector files in build.
Marked as failing in <http://trac.webkit.org/r155746>.
Closing as invalid, as this bug pertains to the old inspector UI and/or its tests.
Please file a new bug (https://www.webkit.org/new-inspector-bug) if the bug/feature/issue is still relevant to WebKit trunk.