A Study Evaluating Atezolizumab, With or Without Bevacizumab, in Participants With Unresectable Hepatocellular Carcinoma and Child-pugh B7 and B8 Cirrhosis

General Inclusion Criteria: * Locally advanced or metastatic and/or unresectable HCC with diagnosis confirmed by histology/cytology or clinically by American Association for the Study of Liver Diseases (AASLD) criteria in cirrhotic participants * Disease that is not amenable to curative surgical and/or locoregional therapies * No prior systemic treatment (including systemic investigational agents) for locally advanced or metastatic and/or unresectable HCC * Measurable disease (at least one untreated target lesion) according to Response Evaluation Criteria in Solid Tumors, Version 1.1 (RECIST v1.1) * Eastern Cooperative Oncology Group (ECOG) performance status of 0-2 within 7 days prior to initiation of study treatment * Child-pugh B7 or B8 cirrhosis at screening and within 7 days prior to study treatment * Adequate hematologic and end-organ function * Life expectancy of at least 12 weeks * Female participants of childbearing potential must be willing to avoid pregnancy and egg donation * Absolute neutrophil count ≥1.0 x 10\^9 per liter (/L) (≥1000 per microliter \[/μL\]) without granulocyte colony-stimulating factor support * Platelet count ≥ 50 × 109/L (50,000/μL) without transfusion * Hemoglobin ≥ 80 grams per liter (g/L) (8 grams per deciliter \[g/dL\]) aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤ 5 × upper limit of normal (ULN) * Serum bilirubin ≤ 3 × ULN * Creatinine clearance ≥ 50 milliliters per minute (mL/min) (calculated using the Cockcroft-gault formula) * Serum albumin ≥ 20 g/L (2.0 g/dL) without transfusion in the prior 3 months * International normalized ratio (INR) ≤2.3 General Exclusion Criteria: * Pregnancy or breastfeeding * Prior treatment with cluster of differentiation 137 (CD137) agonists or immune checkpoint blockade therapies * Treatment with investigational therapy within 28 days prior to initiation of study treatment * Treatment with locoregional therapy to liver within 28 days prior to initiation of study treatment, or non-recovery from side effects of any such procedure * Treatment with systemic immunostimulatory agents * Treatment with systemic immunosuppressive medication * Treatment with a live, attenuated vaccine within 4 weeks prior to initiation of study treatment * Inadequately controlled hypertension * Active or history of autoimmune disease or immune deficiency * History of idiopathic pulmonary fibrosis, organizing pneumonia, drug-induced pneumonitis, or idiopathic pneumonitis, or evidence of active pneumonitis on screening chest computed tomography (CT) scan * Participants who have a known concurrent malignancy that is progressing or requires active treatment, who have not completely recovered from treatment, or who have a significant malignancy history that, in the opinion of the investigator, should preclude participation * Participants on preventative hormonal therapies (i.e., tamoxifen and other hormonal inhibitors) are not excluded * Known fibrolamellar HCC, sarcomatoid HCC, other rare HCC variant, or mixed cholangiocarcinoma and HCC * Symptomatic, untreated, or actively progressing central nervous system (CNS) metastases * Prior allogeneic stem cell or solid organ transplantation * Actively listed for liver transplantation * Co-infection with hepatitis B virus (HBV) and hepatitis C virus (HCV) * Untreated or incompletely treated esophageal and/or gastric varices with bleeding or that are at high risk for bleeding * A prior bleeding event due to esophageal and/or gastric varices within 6 months prior to initiation of study treatment * Grade ≥3 hemorrhage or bleeding event within 6 months prior to initiation of study treatment * Hepatic encephalopathy is allowed if no active symptoms or stable within 3 months of study treatment * History, planned, or recommended placement of transjugular intrahepatic portosystemic shunt (TIPS) is excluded from Cohort A only. TIPS is acceptable in Cohort B * Diagnostic paracentesis is allowed. Therapeutic paracentesis: one large volume paracentesis prior to enrollment with diuretic controlled ascites is allowed. * Participants with ascites controlled on diuretics are allowed * History of spontaneous bacterial peritonitis within last 12 months