Study of Cobimetinib in Combination With Atezolizumab and Bevacizumab in Participants With Gastrointestinal and Other Tumors

Inclusion Criteria:

* Eastern Cooperative Oncology Group performance status of 0 or 1
* Histologically confirmed unresectable metastatic colorectal adenocarcinoma
* Life expectancy at least 12 weeks
* Progression on a prior line of therapy that contained a fluoropyrimidine and oxaliplatin or irinotecan for unresectable metastatic colorectal adenocarcinoma
* Measurable disease per RECIST v1.1
* Adequate hematologic and end organ function
* Creatinine clearance greater than or equal to (\>=) 30 milliliters per minute (mL/min)
* For biopsy cohort, participants must be bevacizumab naive or received the last bevacizumab treatment at least 12 months prior to Cycle 1 Day 1 and according to the investigator's judgment the planned biopsies would not expose participants to substantially increased risk of complications
* For women of childbearing potential, agreement to remain abstinent (refrain from heterosexual intercourse) or use of contraceptive methods that result in a failure rate of less than (\<) 1 percent (%) per year during the treatment period and for at least 180 days after the last study treatment
* For men, agreement to remain abstinent (refrain from heterosexual intercourse) or use contraceptive measures, and agreement to refrain from donating sperm

Exclusion Criteria:

* More than one prior line of systemic therapy for advanced CRC
* Participants with known microsatellite (MSI)-high status
* Major surgery or significant traumatic injury within 60 days prior to enrollment
* Minor surgical procedure within 15 days of study Cycle 1 Day 1
* Untreated central nervous system (CNS) metastases
* Treatment with any investigational agent or approved therapy within 28 days
* Malignancies other than colorectal cancer within 5 years prior to Cycle 1 Day 1
* Prior radiation therapy within 30 days prior to study Cycle 1 Day 1 and/or persistence of radiation-related adverse effects
* Prior allogeneic bone marrow transplantation or solid organ transplant for another malignancy in the past
* Spinal cord compression not definitively treated with surgery and/or radiation
* Uncontrolled pleural effusion, pericardial effusion, or ascites requiring recurrent drainage procedures
* Current or recent use of therapeutic oral or parenteral anticoagulants or thrombolytic agents
* Intake of St. John's wort or hyperforin (potent cytochrome P450 \[CYP\] 3A4 enzyme inducer) or grapefruit juice (potent CYP3A4 enzyme inhibitor) within 7 days prior to initiation of study treatment
* History of severe allergic, anaphylactic, or other hypersensitivity reactions to chimeric or humanized antibodies or fusion proteins
* Known hypersensitivity or allergy to biopharmaceuticals produced in Chinese hamster ovary cells or any components of cobimetinib, atezolizumab, or bevacizumab formulations
* Prior treatment with clusters of differentiation (CD) 137 (CD137) agonists or immune checkpoint blockage therapies, anti-programmed death protein-1, anti-program death-ligand 1, mitogen-activated protein kinase (MEK) inhibitor
* Proteinuria value \> 1.0 g at screening
* Uncontrolled glaucoma with intraocular pressure ≥ 21 mmHg
* Hyperglycemia (fasting) ≥ Grade 2
* Human Immunodeficiency Virus (HIV) infection
* Active hepatitis B or hepatitis C
* History of autoimmune disease, clinically significant cardiac or pulmonary dysfunction
* Administration of a live, attenuated vaccine within 4 weeks prior to Cycle 1 Day 1 or at any time during the study and for at least 5 months after the last dose of study drug
* History of or evidence of retinal pathology on ophthalmologic examination that is considered a risk factor for neurosensory retinal detachment/central serous chorioretinopathy, retinal vein occlusion, or neovascular macular degeneration
* History of idiopathic pulmonary fibrosis, organizing pneumonia, drug-induced pneumonitis, or idiopathic pneumonitis
* Uncontrolled tumor pain