merge_pr_48989

Add attribute reflection behavior for dialog closedBy [2/N]

This implements reflection of closedBy including the "limited to
known values" behavior.

See spec PR for details:
whatwg/html#10737

Bug: 376516550
Change-Id: Iddefd573fe19fd39f4b3aebe13390235fea969b9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5988652
Commit-Queue: Mason Freed [email protected]
Reviewed-by: David Baron [email protected]
Commit-Queue: David Baron [email protected]
Auto-Submit: Mason Freed [email protected]
Cr-Commit-Position: refs/heads/main@{#1379228}