Additional Study Information: The purpose of this study is to compare any good and bad effects of using atezolizumab alone or with another drug called cobimetinib. About 82 people are expected to taking part in this study. Adding cobimetinib to atezolizumab could help to shrink your cancer, but it could also cause extra side effects. This study will allow the researchers to know whether cobimetinib plus atezolizumab is better, the same, or worse than using atezolizumab alone. To be better, the two study drugs together should delay the cancer by two or more months compared to atezolizumab alone. The hemotherapy drugs, atezolizumab and cobimetinib, are already FDA-approved for treating other cancers, but they have not been studied in this kind of cancer. Therefore, these drugs are considered investigational. Another purpose of this study is for researchers to learn more about how the study drugs might affect the immune system to help fight your cancer.