Assigning different ringtone for non-contacts

I'm using iOS 9.1 and I want to assign one ringtone for all known contacts and a different one for non-contacts.

I also have another ringtone for a few specific contacts, but in general I want to know if the person who's calling is on my contact list.

How can this be achieved without any jailbreaks or the like ?

I'm also aware that I could just define a ringtone for my entire contacts list. But this is just inconvenient. Every time I add a contact on my Google Account I would have to assign the ringtone on the iPhone.

I have assigned the same ringtone to everyone in my contact list, and it took days. Then I selected a different default ringtone, and I know that when I hear this, the caller is not a contact. But I would suggest adding this feature for iPhone 7, because it's important.