This study will evaluate the preliminary efficacy, safety, and pharmacokinetics of cobimetinib and atezolizumab in participants with advanced BRAF V600-wild type (WT), metastatic, or unresectable locally advanced melanoma who have progressed on prior anti−PD-1 therapy. In addition, this study will evaluate the efficacy, safety, and pharmacokinetics of atezolizumab monotherapy in participants with BRAFV600-WT metastatic or unresectable locally advanced melanoma, who have not been previously treated.