RenderMathMLRow::firstLineBaseline already provides the correct calculation of ascent for non-empty menclose. Empty menclose are not used in practice so the calculation is irrelevant but aligning on mrow seems fine.
This will allow to get rid of the m_ascent member and will help to keep good vertical alignment of the 'D' in bug 161126.
Created attachment 286838 [details]
Comment on attachment 286838 [details]
View in context: https://bugs.webkit.org/attachment.cgi?id=286838&action=review
> + calculated value is irrelevant. Aligning on mrow (i.e. leaving firstLineBaseline undefined)
Here it's actually "to 0" rather than "undefined".
Committed r205099: <http://trac.webkit.org/changeset/205099>