Count discarded attr() functions with valid argument grammar

<attr-args> = attr( <declaration-value>, <declaration-value>? )

Bug: 491166375
Change-Id: Iefcc43a08f4ea7fd78e3fe7617e89101c61d1557
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7665807
Reviewed-by: Anders Hartvoll Ruud <andruud@chromium.org>
Commit-Queue: Munira Tursunova <moonira@google.com>
Cr-Commit-Position: refs/heads/main@{#1600473}
NOKEYCHECK=True
GitOrigin-RevId: 4c758cc4a92a0fb6377e4a5a2ef4acf81dfeeb6b