[css-containment][css-display] Layout containment on display: contents and display: run-in

Hi www-style,

I'm implementing 'contain: layout' in Gecko right now. One of my test cases
set 'display: contents' on a 'contain: layout' element.

I don't see any obvious way for this to work. What should happen in this
case?

Similarly, it's not clear how 'contain: layout' should be applied to a
'display: run-in' element, since its layout depends on whether it contains
a block.

Should FCification take care of these cases? If so, how?

Thanks!