Navigation: Add optimization to ignore duplicate navigations

[llannasatoll]

This change adds an optimization to the navigate algorithm to ignore duplicate navigations.

As proposed in #11743, this prevents an ongoing navigation from being unnecessarily canceled by a new, identical navigation that is initiated in quick succession (e.g., from an accidental double-click).

• At least two implementers are interested (and none opposed):
  • Chromium (#11743)
  • …
• Tests are written and can be reviewed and commented upon at:
  • https://chromium-review.googlesource.com/c/chromium/src/+/5856811
• Implementation bugs are filed:
  • Chromium: https://crbug.com/366060351
  • Gecko: …
  • WebKit: …
• Corresponding HTML AAM & ARIA in HTML issues & PRs:
• MDN issue is filed: …
• The top of this comment includes a clear commit message to use.

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/browsing-the-web.html ( diff )

[rakina]

I think the "navigation conditions potentially changed" flag should be a property of the "navigable" instead of on the active document, declared here. It should be associated with the ongoing navigation, which means we set it to false whenever we set the ongoing navigation is set / reset. Then in https://html.spec.whatwg.org/multipage/dom.html#dom-document-cookie mention that setting the cookie will set the flag to false, and add a note that other cookie-setting operations such as the Cookie Store API and setting non-HTTP only cookies via fetch can also set the flag to false.