add tests for constructed stylesheet invalidation
When experimenting with constructed CSSStyleSheets I noticed they don't always invalidate properly in Safari, so here are some tests that assert on style invalidation in various forms.
In Safari, this issue exists when working with a StylePropertyMap as well (i.e. the styleMap property for the CSSStyleRule instead of style using a slightly different API), would it make sense to add the tests for that here too?
Is there a WebKit bug filed?
Just filed https://bugs.webkit.org/show_bug.cgi?id=269717
LGTM with a few comments (although I'd be interested to see the results for Chrome and Firefox, but they don't seem to be available yet)
I tested locally and Chrome & Firefox both pass all 3. Safari fails the third, for me.