Cobimetinib (Targeted Therapy) Plus Atezolizumab (Immunotherapy) in Participants With Advanced Melanoma Whose Cancer Has Worsened During or After Treatment With Previous Immunotherapy and Atezolizumab Monotherapy in Participants With Previously Untreated Advanced Melanoma

Inclusion criteria Disease-Specific Inclusion Criteria: Cohorts A and B: * Histologically confirmed Stage IV (metastatic) or unresectable Stage IIIc BRAF V600 WT (locally advanced) melanoma * Documentation of BRAF V600 mutation-negative status in melanoma tumor tissue (archival \[\< 5 years old\] or newly obtained) through use of a clinical mutation test approved by the local health authority * Measurable disease according to Response Evaluation Criteria in Solid Tumors (RECIST) v1.1 * Disease progression on or after treatment with a programmed death (PD)-1 inhibitor either as monotherapy or in combination with other agent(s) Additional Disease-Specific Inclusion Criteria in Cohort B (Biopsy Cohort): * Progressed on or after anti-PD-1 therapy within 12 weeks before study start * Received a minimum of two cycles of anti-PD-1 therapy * Meet the following criteria for resistance to an anti-PD-1 agent: primary resistance defined as disease progression, according to RECIST v1.1, as best response; secondary resistance defined as disease progression after initial confirmed response according to RECIST v1.1 * Consent to undergo tumor biopsies of accessible lesions, before and during treatment and at radiographic progression, for biomarker analyses. * Have at least two accessible lesions that are amenable to excisional or core-needle (minimum three cores and minimum diameter 18 gauge; however, 16 gauge is desirable) biopsy without unacceptable risk of a major procedural complicati…