[css-flexbox] max-content main-size contribution of stretched items with aspect ratio in a definite container #10619

We define the max-content contribution of a flex item in https://drafts.csswg.org/css-sizing-3/#intrinsic-contribution but that definition doesn't account for the stretching effects in flexbox.

Example: finding the max-content size of:

<div style="display: flex; height: 50px"><img src="aspect ratio 1/2"></div>

If the img had a 100% height, it would be defined (because we defer to CSS2 behavior), but stretching isn't handled by CSS2.