We have a fast path to return None if we have no rules for the pseudo-element at
all, but we should also return None if we have no _matching_ rules for it for
the given originating element. This is relied on by consumers like
Servo_ResolvePseudoStyle, which needs to be able to detect the "no styles for
this pseudo-element for this originating element case", to support probing for
whether work for a specific pseudo-element should be done at all.
<!-- Please describe your changes on the following line: -->
---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [ ] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).
<!-- Either: -->
- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because _____
<!-- Also, please make sure that "Allow edits from maintainers" checkbox is checked, so that we can help you if you get stuck somewhere along the way.-->
<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->
Source-Repo: https://github.com/servo/servo
Source-Revision: 04aac0247aea29e361589a75954b4f769478dd02
1f3dc4442d