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This implements the [CSSOM StyleSheet.disabled](https://drafts.csswg.org/cssom/#dom-stylesheet-disabled) IDL attribute.
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- [X] `./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).
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Source-Repo: https://github.com/servo/servo
Source-Revision: c1c3974fb2d8ca60f2837ccd7d2d3b345e440af8