DOSE ESCALATION PHASE: Patients receive atezolizumab intravenously (IV) over 30-60 minutes on day 1. Treatment repeats every 3 weeks for 6 courses in the absence of disease progression or unacceptable toxicity. Within 24-48 hours after receiving atezolizumab, patients also undergo 4-5 fractions of stereotactic body radiation therapy over days 1-5 of course 3.