But not always, I guess.

This line doesn't do anything for constructed stylesheets.

For most of the notifications I think that is just fine, because they'll notify the adopters which most of the time would end up in RecordShadowStyleChange as needed (or notifying the document itself).

But there's one event for which we differ in behavior, which is ShadowRoot::StyleSheetApplicableStateChanged. This one is interesting because it fires events and what not so you don't really want to call it more than once. So gotta be careful on the solution.

These events are only relevant for devtools, so probably not the highest priority.

Or I guess, for that same reason, that that is mostly relevant to the ApplicableStateChanged event and we can just move that bit there.

Ah, we don't even use that for ApplicableStateChanged... So maybe it's just redundant most of the time for stylesheets in shadow dom too...

This should have no behavior change, but makes the setup simpler and
more similar to the constructable sheets.

Depends on D71261

https://hg.mozilla.org/mozilla-central/rev/2fa9eb024124