I've yet to see a *really* mini multi tool that includes a chain breaker, but I have a Topeak Mini 20 Pro, and I do believe it's one of the lightest multi tools available that also includes a chain breaker. It's a great tool and not terribly expensive, and the polished finish is quite blingy. It might be too heavy if you're looking for something along the lines of those really slim multi tools though.

Looks like it may be discontinued, unfortunately. There's one called the Topeak Mini 18, which you might think would be a bit lighter, but it's actually heavier than the Mini 20.