add unload permissions-policy feature

[fergald]

This PR is not at the point where it can be accepted and is currently for reference only.

Add unload as a feature controlled by Permissions-Policy. Unload events are not fired for documents where this feature is enabled.

Explainer: https://github.com/fergald/docs/blob/master/explainers/permissions-policy-unload.md

• [ ] At least two implementers are interested (and none opposed):
  • Chrome
• [ ] Tests are written and can be reviewed and commented upon at:
  • Pending
• [ ] Implementation bugs are filed:
  • Chrome: https://crbug.com/1324111

(See WHATWG Working Mode: Changes for more details.)

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/browsing-the-web.html ( diff ) /infrastructure.html ( diff )