Baseline of overflow non-visible inline blocks

[gsnedders]

From https://lists.w3.org/Archives/Public/www-style/2015Apr/0144.html:

• RESOLVED: Accept Myles' proposal to make baseline of overflow non-visible inline blocks the higher of the actual baseline (at initial scroll position) and the margin-box bottom. Separately investigate whether to switch from margin-box bottom to padding-box bottom for sanity. (requries web-compat check)

@litherum had posted, at the point of the telecon, a proposal and an updated proposal.

The CSS 2.1 errata from this is https://www.w3.org/Style/css2-updates/REC-CSS2-20110607-errata.html#s.10.8.1, which appears to be @litherum's original proposal and not the updated one. Probably should've been the later one!