RenderMathMLOperator used to destroy its descendants and to replace them with an anonymous text node wrapped inside anonymous blocks. After r202420, it just behaves as any other token elements. Hence the code in AccessibilityRenderObject::textUnderElement to handle this specific render tree structure is never executed and can be safely removed.
Created attachment 282232 [details]
Committed r202562: <http://trac.webkit.org/changeset/202562>