Eric Schmidt once ran Google with Sergey Brin at his side. The two men helped turn a Stanford research project into a global force. Now they stand on opposite sides of a bitter dispute inside one of the most expensive ballot battles California has ever seen. Brin, the Google co-founder with a fortune north of $260 billion, has poured more than $100 million into Building a Better California. The group’s stated goal was simple. Stop Proposition 40…