Unset is_modal flag when modal dialog is removed from the document

[sefeng211]

#5936 introduced a side effect that made the modal dialog to keep its modal status when it's being removed from the DOM by using the is modal flag.

This introduces an inconsistency between top layer and modal dialog, as dialog can now have modal status but not in top layer.

This feels weird because we now have two concepts. We can't use the modal status of the dialog to figure out if it's in top layer. In Gecko, now we need to introduce a new internal selector to reflect whether we are in top layer, because we can't use modal status anymore.

How about we also unset it when the element is being removed from the document?

cc @emilio @bfgeek

[josepharhar]

I have a patch for chrome ready, as per the filed chrome bug.
I'll wait for the WPT to land before merging it.

[domenic]

I'm now wondering why we have the "is modal" flag at all, instead of just using "in the top layer" to define the CSS rendering?

I guess because fullscreen also puts the dialog in the top layer, and we don't want fullscreen dialogs to render that way? But does that mean Gecko needs to have a separate flag anyway?

[sefeng211]

Yeah, fullscreen is a case, where dialog is in top layer but not modal. And that's right, we don't just have one flag to indicate both top layer and modal status, however, the thing we are trying to fix here is that modal status should always imply top layer. Currently, there's a discrepancy such that dialog can have modal status without being in top layer. Am I clear....?

[domenic]

Yep, that makes sense. And indeed, unifying would be nice. I'll go poke the PR thread...

[josepharhar]

The chromium patch has been merged