Add test for cloned box-shadow.
This has already been working for some time, but there was no test
coverage.
Bug: 40415661
Change-Id: I796533abc7507cfe69ffae3cc9a58a5ba3f29eb3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5797219
Reviewed-by: Ian Kilpatrick ikilpatrick@chromium.org
Commit-Queue: Morten Stenshorne mstensho@chromium.org
Cr-Commit-Position: refs/heads/main@{#1344189}