Fix parsing grammar in attr()
attr = attr(,) and attr = attr( ,)
should be allowed according to attr()'s grammar, see [0]:
attr() = attr( ? , ?)
[0] https://drafts.csswg.org/css-values-5/#attr-notation
Bug: 40320391
Change-Id: Ia39ee5e79fdfdb70cde166c2bdf00140b6fdcd41
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5854326
Reviewed-by: Anders Hartvoll Ruud andruud@chromium.org
Commit-Queue: Munira Tursunova moonira@google.com
Cr-Commit-Position: refs/heads/main@{#1355085}