In r54084 the contents of the source view in the Resources pane is completely hidden from accessibility tools. Mac OS X's Accessibility Inspector appears to consider that area on-screen to be a black hole. Previous versions of the inspector were not great with accessibility, but at least the content was available in some form.
<rdar://problem/7594378>
Fixed in http://trac.webkit.org/changeset/54133. https://bugs.webkit.org/show_bug.cgi?id=34400