Bug 1811354 [wpt PR 38071] - Add 'no url function' support in css image-set, a=testonly

Bug 1811354 [wpt PR 38071] - Add 'no url function' support in css image-set, a=testonly

Automatic update from web-platform-tests
Add 'no url function' support in css image-set

Currently, if the url of an image-set option is specified as a string
without the 'url()' function notation, parsing fails.

Based on the spec, the url can be just a string.

Spec definition:

"The syntax for image-set() is:

<image-set()> = image-set( <image-set-option># )
<image-set-option> = [ <image> | <string> ]
                     [ <resolution> || type(<string>) ]

Each <string> inside image-set() represents a <url>."

https://w3c.github.io/csswg-drafts/css-images-4/#image-set-notation

With this change Chrome will match the spec as well as Firefox for
both standard and '-webkit-' prefixed syntax.
Safari does not allow empty strings for standard syntax, and does not
allow strings for '-webkit-' prefixed syntax because of [1] and fixed
in [2].
The issue observed in Safari of "showing the missing image icon" is
not observed in Chrome.

[1] https://bugs.webkit.org/show_bug.cgi?id=206909
[2] https://github.com/WebKit/WebKit/commit/bfc08b19e20ed4bf9a9769b14f192843bf7e6fbe

R=futhark, masonf, pdr, nrosenthal

Bug: 1400901
Change-Id: Iaf7e4b3128153664f3d311384b77b025d27bbf6e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4179000
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Commit-Queue: Traian Captan <tcaptan@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1095212}

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wpt-commits: 8b30abf7576afc14a61cc7e1e8679d9be6eea86e
wpt-pr: 38071