merge_pr_50136

Add test for resolving rlh on the :root element

There was only coverage for testing rlh on the :root element for the
font and line-height properties, not other lengths.

Change-Id: Ib67faf7f78d657c7bdf917a32eb7f5786916db98
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6169143
Commit-Queue: Rune Lillesveen [email protected]
Reviewed-by: Anders Hartvoll Ruud [email protected]
Cr-Commit-Position: refs/heads/main@{#1407838}