Don't use it yet (since I was working from a Servo tree). Will hook it up and improve in the Gecko bug.
Right now it takes a `StyleRuleCascadeData`, which means that if all the origins in the document have state selectors we could do just one walk over the tree and not multiple, that will be improved.
Other than that, this is completely untested of course, but I prefer to land it, given I don't think it's complex, and work on the Gecko integration separately. The reason for this is that I also plan to fix the `<slot>` bugs, which will change `StyleRuleCascadeData` and such, and I want the two bugs to conflict as little as possible.
Source-Repo: https://github.com/servo/servo
Source-Revision: 50e4171958d4ff7f1c76d133a8f89e7d5995376f
This is the first step in reusing the invalidation machinery for other stuff,
potentially including QuerySelector / QuerySelectorAll.
Source-Repo: https://github.com/servo/servo
Source-Revision: a89a76e1fc138bd1a60ee974abfc47a4b0f69c09
