If you are found to be eligible to take part in this study, you will first have a "Run-In" period. On Days 1-21 of the Run-In Period, you will receive vemurafenib and cobimetinib. You will take vemurafenib by mouth 2 times each day, about 12 hours apart each time. You will take cobimetinib by mouth 1 time each day. On Days 22-28 of the Run-In Period, you will continue taking a lower dose of vemurafenib, but you will not receive cobimetinib.