This phase III trial is trying to understand how safe and effective immunotherapy (atezolizumab) in combination with targeted therapy (cobimetinib and vemurafenib), compared to a placebo in combination with targeted therapy, is in people with previously untreated BRAFv600 mutation-positive metastatic or locally advanced melanomaA Phase III, Double-Blinded, Randomized, Placebo-Controlled Study of Atezolizumab Plus Cobimetinib and Vemurafenib Versus Placebo Plus Cobimetinib and Vemurafenib in Previously Untreated BRAFV600 Mutation-Positive Patients With Unresectable Locally Advanced or Metastatic Melanoma

Exclusion

Cancer-Related Exclusion Criteria:

• Major surgical procedure within 4 weeks prior study treatment initiation
• Traumatic injury or palliative radiotherapy within 2 weeks prior study treatment initiation
• Active malignancy (other than BRAFv600 mutation-positive melanoma) or malignancy within 3 years prior to screening are excluded, with the exception of resected melanoma, resected basal cell carcinoma (BCC), resected cutaneous squamous cell carcinoma (SCC), resected carcinoma in situ of the cervix, resected carcinoma in situ of the breast, in situ prostate cancer, limited-stage bladder cancer, or any other curatively treated malignancies from which the participant has been disease-free for at least 3 years

Ocular Exclusion Criteria:

• 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 (RVO), or neovascular macular degeneration

Cardiac Exclusion Criteria:

• History of clinically significant cardiac dysfunction
• Left ventricular ejection fraction (LVEF) below the institutional lower limit of normal or below 50%

Central Nervous System (CNS) Exclusion Criteria:

• Untreated or actively progressing CNS lesions (carcinomatous meningitis)
• History of metastases to brain stem, midbrain, pons, or medulla, or within 10 millimeter (mm) of the optic apparatus (optic nerves and chiasm); or leptomeningeal metastatic disease; or intracranial hemorrhage

Additional Exclusion Criteria:

• Uncontrolled diabetes or symptomatic hyperglycemia
• Current severe, uncontrolled systemic disease (including, but not limited to, clinically significant cardiovascular, pulmonary, or renal disease) other than cancer
• History of malabsorption or other clinically significant metabolic dysfunction
• Pregnant or breastfeeding, or intending to become pregnant during the study
• Prior allogeneic stem cell or solid organ transplantation
• History of idiopathic pulmonary fibrosis, organizing pneumonia (example: bronchiolitis obliterans), drug-induced pneumonitis, or idiopathic pneumonitis, or evidence of active pneumonitis on screening chest computed tomography (CT) scan
• Active or history of autoimmune disease or immune deficiency
• Known clinically significant liver disease, inherited liver disease and active viral disease
• Active tuberculosis
• Treatment with therapeutic oral or intravenous (IV) antibiotics; or with a live, attenuated vaccine; or systemic immunosuppressive medication
• Known hypersensitivity to biopharmaceutical agents produced in Chinese hamster ovary cells or any component of the atezolizumab, cobimetinib, or vemurafenib formulations
• Any grade >/=3 hemorrhage or bleeding event within 4 weeks prior to initiation of study treatment
• History of stroke, reversible ischemic neurological defect, or transient ischemic attack within 6 months prior to initiation of study treatment