It's possible we have some other code that makes things work when OOP frames are involved, but I'm not sure.

Note this also includes use of functions like GetRootDocument, which does the same thing indirectly.

Henri, could you look into figuring this out for Fission-compatibility?

(hsivonen is on pto for couple weeks still, so I can look at this)

FullscreenChange doesn't have any GetInProcessParent usage. It is unclear to me what this bug is about.

(In reply to Olli Pettay [:smaug] from comment #3)

(hsivonen is on pto for couple weeks still, so I can look at this)

FullscreenChange doesn't have any GetInProcessParent usage. It is unclear to me what this bug is about.

I think the main issue is the use of nsContentUtils::GetRootDocument in the fullscreen code in Document.cpp, which uses GetInProcessParent indirectly, but there are also some direct usages: https://searchfox.org/mozilla-central/rev/82c04b9cad5b98bdf682bd477f2b1e3071b004ad/dom/base/Document.cpp#12995,13031

Alphan has been looking into Fullscreen Fission issues. I believe we can start with Alphan. Thank you. :)

There are three parts for fullscreen code in Document.cpp.

I think the main issue is the use of nsContentUtils::GetRootDocument in the fullscreen code in Document.cpp, which uses GetInProcessParent indirectly,

1. The usage of nsContentUtils::GetRootDocument in FullscreenRoots.
   https://searchfox.org/mozilla-central/rev/03794edd6edcc3fc1e222de966cb27256ce08998/dom/base/nsContentUtils.cpp#6596
   https://searchfox.org/mozilla-central/rev/03794edd6edcc3fc1e222de966cb27256ce08998/dom/base/Document.cpp#12934,12960,13200,13826,13924

but there are also some direct usages:

2. The usage of GetInProcessRootTreeItem() and GetInProcessParent() in PendingFullscreenChangeList.
   https://searchfox.org/mozilla-central/rev/82c04b9cad5b98bdf682bd477f2b1e3071b004ad/dom/base/Document.cpp#12995,13031

3. Here is the another usage of GetInProcessRootTreeItem.
   https://searchfox.org/mozilla-central/rev/03794edd6edcc3fc1e222de966cb27256ce08998/dom/base/Document.cpp#13765,13854

I will handle 2 and 3 in Bug 1585074.

There are three parts for fullscreen code in Document.cpp.

I think the main issue is the use of nsContentUtils::GetRootDocument in the fullscreen code in Document.cpp, which uses GetInProcessParent indirectly,

1. The usage of nsContentUtils::GetRootDocument in FullscreenRoots.
   https://searchfox.org/mozilla-central/rev/03794edd6edcc3fc1e222de966cb27256ce08998/dom/base/nsContentUtils.cpp#6596
   https://searchfox.org/mozilla-central/rev/03794edd6edcc3fc1e222de966cb27256ce08998/dom/base/Document.cpp#12934,12960,13200,13826,13924

but there are also some direct usages:

2. The usage of GetInProcessRootTreeItem() and GetInProcessParent() in PendingFullscreenChangeList.
   https://searchfox.org/mozilla-central/rev/82c04b9cad5b98bdf682bd477f2b1e3071b004ad/dom/base/Document.cpp#12995,13031

3. Here is the another usage of GetInProcessRootTreeItem.
   https://searchfox.org/mozilla-central/rev/03794edd6edcc3fc1e222de966cb27256ce08998/dom/base/Document.cpp#13765,13854

I will handle 2 and 3 in Bug 1585074.

This is okay and working in fission due to Alphan's other changes. New tests have been added[1] to verify this and ensure things keep working.

[1] See Bug 1665941 and specifically D90940