Make display:contents map to display:none #90
Description
cc @rwlbuis @bkardell @mrego @emilio
From https://drafts.csswg.org/css-display/#unbox-mathml
For all MathML elements, display: contents computes to display: none.
TODO: check the implementation status in webkit/firefox and write tests for these.
Rob did https://github.com/Igalia/chromium-dev/commit/177eb951392219339c47526c65c1789439a1d6b0