Managed by the owner. Note that switching the Project permissions to "locked" will blow away all existing permissions on content in the project, just like the old button in the same location used to do--so make sure you are certain it's what you want, if you do have content in that project already!

"Managed by owner" is basically the same behavior as pre-9.2: the permissions set for the project are pre-populated, but publisher is allowed to override them.