Code review comment for lp:~nick-dedekind/qtmir/lp1475678.surface-occlude

> One thing to look at is to what happens when MirSurfaceItem::setSurface() is
> called and the MirSurfaceItem in question is already hidden. You have to synce
> the visibility of MirSurface with the one of its MirSurfaceItem inside
> setSurface().

It did already, but I've updated since (view registration).

>
> Another thing to consider is what happens when there are multiple
> MirSurfaceItems displaying the same MirSurface? It will only get occluded if
> *all* items showing it are hidden. In other words: the MirSurface will be
> exposed as long as there's some visible MirSurfaceItem in the scene displaying
> it.

I've added surface visibility aggregation through view registration.