Additional Study Information: The purpose of this study is to find out what effects, whether good or bad, that the combination of MOXR0916 plus atezolizumab has on you and your bladder cancer (locally advanced or metastatic urothelial cancer). Atezolizumab is approved in the United States for subjects with bladder cancer that has worsened after platinum-containing chemotherapy and is being considered for approvals in additional countries and in additional disease settings. MOXR0916 is an experimental drug, and the combination of MOXR0916 and atezolizumab in this research study is experimental, which means that this combination is not approved by health authorities, such as the US Food and Drug Administration (FDA), for the treatment of advanced bladder cancer. In this study, you will receive atezolizumab and either MOXR0916 or a placebo (a substance that looks like MOXR0916 but has no active medication). Both MOXR0916 and atezolizumab drugs are antibodies, which are a type of protein. Your immune system makes antibodies in order torecognize substances that are foreign to your body. MOXR0916 and atezolizumab are antibodies that are manufactured in a laboratory and designed to recognize the targets OX40 and PD-L1, respectively, on human cells. These drugs are given to you by your doctor in the hospital or clinic.