Removing steps on fullscreen element leave a dangling fullscreen flag

[nt1m]

If you have a fullscreen element, then move it to a different parent, it triggers the removing steps which does at step 3:

1. If node is document’s fullscreen element, exit fullscreen document.
2. Otherwise...
3. If document’s top layer contains node, remove node from document’s top layer.

But in the exit fullscreen algorithm, the fullscreen flag is only removed at step 14.3. This is problematic, because that step runs in parallel, so step 3.3 of the removing steps which removes the fullscreen element from the top layer will run before.

That means we end up stopping the exit fullscreen at step 11, so we end up never removing the fullscreen flag, which is problematic if the removed element is re-appended in the document.

Chromium handles it specifically at step 7. of exit fullscreen, by invoking the "unfullscreen doc's fullscreen element" as a step 7.2.

[marcoscaceres]

@foolip, do you by chance know the history of "Step 7.2" (see Chrome's implementation) and why it's no longer in the spec?

WebKit will follow Chrome's behavior as otherwise it affects YouTube, but it would be good to figure this out as, right now, the we both don't follow the spec.

[foolip]

Sorry @nt1m @marcoscaceres, I missed this back when it was filed. I'll go through all open issues to see what else I've neglected.

Step 7.2 in Chromium comes from https://source.chromium.org/chromium/chromium/src/+/14eeb1d5b6369a4fefa57973bf6b646469f72e35 by @dtapuska. It was never landed in the spec, but it was in #128, where I argued that we shouldn't have that step. I don't remember the details, but in the end we landed the PR without that step, with #133 filed as a follow-up.

Since that step is still what shipped, I think adding it to the spec is the correct first step for sure.