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~~This should help #11203~~ (no, it doesn't, but still worth it).
r? @jdm
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Source-Repo: https://github.com/servo/servo
Source-Revision: 5d98ee61bbdb76e179bc62c0366438e28abe79a9
I updated the `WebIDL.py` from latest mozilla-central. And add a `./mach test-webidl` command. For #9397
Source-Repo: https://github.com/servo/servo
Source-Revision: 0ada7f9c8eda9879b5536cea3266c94214f9ce9b