Modifications made to this test for https://bugs.webkit.org/show_bug.cgi?id=88473 are causing it to fail most (but not all) of the time on the Mac bots. When it fails, it fails because "Panel shown" sometimes happens before "Extension panel size correct" instead of after. I'm going to skip it for now.
<rdar://problem/11731566>
Skipped test with http://trac.webkit.org/changeset/121067
Should be fixed by r122216: http://trac.webkit.org/changeset/122216