While working on this CL:
https://chromium-review.googlesource.com/c/chromium/src/+/1281702, I found that there might be a bug in the implementation of the CSSPropertyID hash traits. The problem was that I was not able to insert an entry into a HashMap<CSSPropertyID, String>

I created a unit test:
https://chromium-review.googlesource.com/c/chromium/src/+/1388288
that didn't fail.

It might be worth to investigate what the problem is.