If you are enrolled in Group A, the dose of cobimetinib you receive will depend on when you join this study. The first group of participants will receive the highest dose level of cobimetinib. The next new group will receive the same dose of cobimetinib if no intolerable side effects were seen. If intolerable side effects were seen, then the next new group will receive a lower level dose. This will continue until the highest tolerable dose of cobimetinib is found.