Improve comments/code/tests related to allowing :is()/:not()/:where() after ::part().
This is expected to have no behavior change.
This updates comments, adds tests, and corrects the return value of
CSSSelector::IsAllowedAfterPart() to reflect that these pseudos are
allowed after ::part().
The code change to CSSSelector::IsAllowedAfterPart does not appear to be
needed; the selectors were already allowed. However, it seems like
CSSSelector::IsAllowedAfterPart may as well tell the truth.
The change to CSSSelector::IsAllowedAfterPart is behind the (status:
experimental) CSSPartAllowsMoreSelectorsAfter flag, along with other
changes.
Bug: 40623497, 40277472
Change-Id: I47da85fff8be6a4555487e46b5b2062cf2f112bc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5812213
Reviewed-by: Rune Lillesveen futhark@chromium.org
Commit-Queue: David Baron dbaron@chromium.org
Cr-Commit-Position: refs/heads/main@{#1347348}