ARM III: Patients receive obinutuzumab IV on day 1, cyclophosphamide IV over 15 minutes on day 1, doxorubicin hydrochloride IV on day 1, vincristine sulfate IV on day 1, and prednisone PO on days 1-5. Treatment with obinutuzumab repeats every 21 or 28 days for up to 12 courses in the absence of disease progression or unacceptable toxicity. Treatment with combination chemotherapy repeats every 21 days for up to 6 courses in the absence of disease progression or unacceptable toxicity.