Left and right padding should be 0 on an mrow element. See the link to the MathML 3 test suite.
Created attachment 64210 [details] Patch Patch + updated layout tests
Comment on attachment 64210 [details] Patch Clearing flags on attachment: 64210 Committed r65275: <http://trac.webkit.org/changeset/65275>
All reviewed patches have been landed. Closing bug.