Remove image/media origins and check origin-cleanness directly

[domenic]

That is, check the type of response directly, instead of synthesizing an opaque origin for opaque responses and then comparing that to the entry settings object's origin.

This helps with #1431 by removing various uses of the entry concept, and closes #2761 by removing the origin concept for image and media elements entirely, since it is now unused.

• At least two implementers are interested (and none opposed):
  • By code inspection this matches Chromium
  • I strongly suspect this also matches other browsers
• Tests are written and can be reviewed and commented upon at:
  • I suspect this is tested in depth. I'm not 100% sure when the old model differs from the one proposed here. I'd like to ask that we don't make me test it since this is so much clearly more correct and probably these sorts of security-sensitive areas have a lot of tests already.
• Implementation bugs are filed:
  • N/A

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

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/canvas.html ( diff )
/imagebitmap-and-animations.html ( diff )
/images.html ( diff )
/origin.html ( diff )

[annevk]

This is amazing. I'm surprised it ended up being such a straightforward patch.

Note that this is also fixes #2813. And given that @jakearchibald might want to look at this or cheer or some such. 😊

[annevk]

Keep the comma?

[jakearchibald]

Yessssss!