[css-flex] min-content size of column-wrap flexboxes.

[bfgeek]

Blink successfully shipped the behaviour for changing the intrinsic size of column wrap flex-boxes in the spec (yay!) see:
https://bugs.chromium.org/p/chromium/issues/detail?id=507397

https://drafts.csswg.org/css-flexbox-1/#intrinsic-cross-sizes

Currently the min-content size is:

The min-content cross size is the largest min-content contribution among all of its flex items.

This is kinda arbitrary for this case. E.g. https://www.software.hixie.ch/utilities/js/live-dom-viewer/?saved=11970

An option (which might not be web-compatible - changing the min-content specifically is risky) is for when a column wrap flexbox has a non-infinite available main size (it is constrained somehow, and lines may wrap) - to make the min-content == max-content. This would reduce the arbitrariness, but render the flexbox "inflexible".