Add onmessageerror to WindowEventHandler
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Add the basics of TextTrack
## Summary
Implement the basics of the TextTrack elements:
- TextTrack
- TextTrackCue
- TextTrackCueList
- TextTrackList
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- [x] These changes is related to #22311
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Make desktop webdriver WPT harness work
This change allows me to run `./mach test-wpt --product servodriver --no-pause-after-test tests/wpt/mozilla/tests/mozilla/DOMParser.html` successfully again.
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- [x] `./mach build -d` does not report any errors
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- [x] These changes fix#22409
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Remove redundant `.clone()`s
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Removes `clone()`s of values unused after cloning.
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Add info about building on Linux Mint to README.md
Linux Mint 19.* is based on Ubuntu 16.04 packages.
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- [X] These changes do not require tests because they are documentation changes in the `README.md`
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Cancel animations that affect nodes that do not participate in layout.
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix#22378
- [x] There are tests for these changes
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