MathML padding overrides only need to be on RenderMathMLRoot
Created attachment 183238 [details] Patch
Actually this whole mechanism (intrinsic padding for MathML) could be removed now, using flexbox's order property instead of absolute positioning, to get <mroot>'s 2nd child (the index) to be placed before the first child (the base, i.e. radicand). (Note this technique also fixes a major limitation of http://www.w3.org/TR/mathml-for-css/#d2e165 for other browser engines.) I recommend this - I know the guys who implemented flexbox in webkit and they're really smart. :)
Comment on attachment 183238 [details] Patch Clearing flags on attachment: 183238 Committed r140032: <http://trac.webkit.org/changeset/140032>
All reviewed patches have been landed. Closing bug.