This is a bug fix for a build failure where the following scenario leads to a deadlock:
T1: Rename command is renaming 'test.coll' to 'test.system.views', so it has the MODE_IX on 'test' and MODE_X on both 'coll' and 'system.views'. The next step is to check if 'coll' is a view by calling the ViewCatalog::lookup() and waiting to acquire the ViewCatalog mutex which is currently held by T2.
T2: Running CountCmd on a collection that didn't exist, but in AutoGetCollection we check if it could be a view and call ViewCatalog::lookup(), here we see that the ViewCatalog is invalidated, so we call _reloadIfNeeded. Now _reloadIfNeeded() uses the DurableViewCatalog::iterate but that requires the MODE_IS lock on the 'test.system.views' collection which is currently held by T1.
So we have a deadlock where:
T1 has MODE_X on 'test.system.views' but is waiting for ViewCatalog mutex.
T2 has ViewCatalog mutex during reload and needs MODE_IS on 'test.system.views'.