A Study of Polatuzumab Vedotin in Combination With Rituximab or Obinutuzumab, Cyclophosphamide, Doxorubicin, and Prednisone in Participants With B-Cell Non-Hodgkin's Lymphoma

Cyclophosphamide will be administered at 750 milligrams per square meter (mg/m\^2) IV every 3 weeks (starting from Cycle 1 Day 1), for 6 or 8 cycles.

Doxorubicin will be administered at 50 mg/m\^2 IV every 3 weeks (starting from Cycle 1 Day 1), for 6 or 8 cycles.

Obinutuzumab will be administered at 1000 milligrams (mg) IV on Cycle 1 Days 1, 8, and 15 and on Day 1 of Cycles 3-8.

Polatuzumab vedotin will be administered at escalating doses (at a starting dose of 1 mg/kg) IV every 3 weeks, for 6 or 8 cycles.

Prednisolone will be administered at 100 mg orally daily for 5 days every 3 weeks (starting from Cycle 1 Day 1), for 6 or 8 cycles. Prednisone at 100 mg orally from Day -7 to Day -1 may be given at the discretion of the treating investigator physician.

Prednisone will be administered at 100 mg orally daily for 5 days every 3 weeks (starting from Cycle 1 Day 1), for 6 or 8 cycles. Prednisone at 100 mg orally from Day -7 to Day -1 may be given at the discretion of the treating investigator physician.

Rituximab will be administered at 375 mg/m\^2 IV every 3 weeks (starting from Cycle 1 Day 1), for 6 or 8 cycles.