A Study of the Safety and Efficacy of Atezolizumab Administered in Combination With Bevacizumab and/or Other Treatments in Participants With Solid Tumors

5-FU (400 mg/m\^2) will be administered as an IV bolus, followed by 2400 mg/m\^2 by continuous IV infusion over 46 (± 1) hours, q2w.

Participants will receive atezolizumab in a flat dose of 1200 mg q3w (Arm A, Group E2, and Arm F) or 840 mg q2w (Arm B, Arm C, and Groups E1 and E3).

Participants will receive bevacizumab at 15 mg/kg q3w (Arm A and Group F1) or 10 mg/kg q2w (Arm B).

Gemcitabine will be administered according to the local prescribing information. The starting dose-level of gemcitabine (1000 mg/m\^2) will be administered intravenously over 35 (± 5) minutes on Days 1, 8, and 15 of each 28-day cycle (3-weeks-on/1-week-off schedule).

Leucovorin 200 mg/m\^2 L-isomer form or 400 mg/m\^2 D,L-racemic form will be administered IV over 120 (± 15) minutes, q2w.

Nab-Paclitaxel will be administered according to the local prescribing information. The starting dose-level of nab-paclitaxel (125 mg/m\^2) will be administered intravenously over 35 (± 5) minutes on Days 1, 8, and 15 of each 28-day cycle (3-weeks-on/1-week-off schedule).

Oxaliplatin 85 mg/m\^2 will be administered IV over 120 (± 5) minutes q2w.

Capecitabine may be administered after 6 months at the discretion of the investigator (range of 650-1000 mg/m\^2) twice daily on Days 1-4 of a 21-day cycle.

Cisplatin will be administered as 80 mg/m\^2 IV over 120 minutes q3w (Group E2).