Build list of selectedcontent elements to clear

[josepharhar]

This PR improves the "clear a select's non-primary selectedcontent elements" algorithm by making it create a list of selectedcontent elements to modify separately from modifying them in order to prevent the list of elements to change while iterating.

Fixes #11880

• At least two implementers are interested (and none opposed):
  • Chromium
  • WebKit
• Tests are written and can be reviewed and commented upon at:
  • https://chromium-review.googlesource.com/c/chromium/src/+/7128135
• Implementation bugs are filed:
  • Chromium: https://issues.chromium.org/issues/458113204
  • Gecko: N/A
  • WebKit: N/A
• Corresponding HTML AAM & ARIA in HTML issues & PRs: not needed
• MDN issue is filed: not needed
• The top of this comment includes a clear commit message to use.

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

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/form-elements.html ( diff )

[annevk]

@josepharhar it doesn't seem like the tests in https://chromium-review.googlesource.com/c/chromium/src/+/7128135 have made their way to WPT. Any reason this appears to be stalled?

[annevk]

Looks good modulo nit, but the test needs sorting out.

[josepharhar]

@josepharhar it doesn't seem like the tests in https://chromium-review.googlesource.com/c/chromium/src/+/7128135 have made their way to WPT. Any reason this appears to be stalled?

Sorry, I will get it reviewed very soon