Percentage height quirk should apply to flex and grid items

[zcorpan]

Fixes w3c/csswg-drafts#5545.

• At least two implementers are interested (and none opposed):
  • See resolution at [css-grid][css-flexbox][quirks] Avoid percentage height quirk in new layout models w3c/csswg-drafts#5545 (comment)
• Tests are written and can be reviewed and commented upon at:
  • TODO
• Implementation bugs are filed:
  • Chromium: …
  • Gecko: …
  • WebKit: …
• MDN issue is filed: N/A
• The top of this comment includes a clear commit message to use.

(See WHATWG Working Mode: Changes for more details.)

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Preview | Diff

[annevk]

Looks good editorially.

[Loirooriol]

Oops, I wrote a review a while ago, but forgot to submit it.

[Loirooriol]

This should be restricting the quirk rather than applying it more frequently...
So we need to return element if some of these conditions holds:

• computed value of position is absolute
• element is not a block box nor an inline-block
• element is a flex item or grid item

The 3rd condition is superfluous, but the CSSWG wanted to be extra explicit 🤷

In CSS2 table wrapper boxes are either block boxes or inline-block boxes as per https://drafts.csswg.org/css2/#model, so I think the above handles them well. If you want to be extra explicit, the 2nd condition should be

• element is not a block box, nor an inline-block, nor a block-level or inline-level table wrapper box

E.g. if we add display: masonry, a masonry-level table wrapper box will not be covered by the 3rd condition, so it should be covered by the 2nd one, so it can't exclude all table wrapper boxes.