Add OptOutError to the error names list

[nickburris]

This PR adds a new OptOutError to the DOMException error names list. We plan to use this error name in the Secure Payment Confirmation API (see issue #1168). Since we don't need any additional attributes (i.e., we don't need a new class interface to extend DOMException), a new error name will suffice. The error name is generic so that it can be used by other APIs with similar use cases.

• At least two implementers are interested (and none opposed):
  • In the short term, this error name will be used by the Secure Payment Confirmation API implemented in Chrome, and can be used in a similar fashion by other APIs.
• Tests are written and can be reviewed and commented upon at:
  • Usage of the error name will be tested by APIs (e.g. Secure Payment Confirmation) that use it.
• Implementation bugs are filed:
  • Chromium: https://bugs.chromium.org/p/chromium/issues/detail?id=1383295
• MDN issue is filed:
  • Will open a PR to add this to https://developer.mozilla.org/en-US/docs/Web/API/DOMException#error_names

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

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Preview | Diff

[nickburris]

PTAL @rsolomakhin / @stephenmcgruer with your SPC API hat on (impl: https://chromium-review.googlesource.com/c/chromium/src/+/4021495)

PTAL @domenic with your webidl spec hat on, + @annevk thank you for your input on the issue, extending the error names list per your recommendation :)

[rsolomakhin]

LGTM!

[domenic]

This LGTM. Even if Secure Payment Confirmation is a single-implementer API, I think we should be lenient with merging values into this table, especially if they're designed to be generic in this way.

/cc @annevk @EdgarChen in case they disagree. I propose we give this a couple days in case others have thoughts then I'll merge.

[annevk]

Yeah I think that's okay. @nickburris should make their membership of the googlers organization public.