Fix #245 - Addressing new popover values

[theIDinside]

Since the popover attribute got a new value, it's
"find topmost popover ancestor" algorithm changed, and this PR attempts to address this in the Fullscreen API specification.

After discussing with @lukewarlow we came to the conclusion that this is probably the intended change for the Fullscreen API spec.

This addresses #245

• At least two implementers are interested (and none opposed):
  • Chromium (already implemented like this)
  • …
• Tests are written and can be reviewed and commented upon at:
  • …
• Implementation bugs are filed:
  • Chromium: …
  • Gecko: …
  • WebKit: …
• MDN issue is filed: …
• The top of this comment includes a clear commit message to use.

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

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Preview | Diff

[lukewarlow]

FYI Reviewers: This is to fix the build as it's currently broken (see #246 for a standalone PR to fix that if that's preferable)

[lukewarlow]

These aren't currently exported so are manually added here. PR to export them: whatwg/html#11140

[theIDinside]

Probably just remove these from this PR then, right?

Nvm :P

[lukewarlow]

Once that gets merged yeah you should be able to remove these, useful to keep them for now so the preview works

[foolip]

This seems to match Chromium's implementation so I'll go ahead and approve it in the interest of progress / matching reality.

I'll comment on whatwg/html#11140 what we could do differently to use a slightly higher level abstraction.

[foolip]

I guess a test is needed for this, testing the interaction of popover=hint and going fullscreen? I think such a test would need to get an element into the "open as hint" state and then fullscreen an ancestor element, and finally check if the popover was closed or not.

[annevk]

A test is needed, but we also can't merge this until the HTML integration situation has an agreed upon solution.