What problem does this solve or what need does it fill?

This is necessary for correctly computing the "min-content" and "max-content" sizes of a flexbox container.

What solution would you like?

Implement §9.9 Intrinsic Sizes of the Flexbox Specification

Tasks:

• §9.9.1 Intrinsic Main Sizes) Implement §9.9.1. Flex Container Intrinsic Main Sizes #354
• §9.9.2 Intrinsic Cross Sizes

What alternative(s) have you considered?

Do nothing and stick with the existing "always shrink to fit" strategy.

Additional context

This was uncovered in testing the integration between Flexbox and CSS Grid.