A Phase III, Open-Label, Multicenter, Randomized Study Evaluating the Efficacy And Safety of MPDL3280A (Anti-PD-L1 Antibody) In Combination With Carboplatin+Paclitaxel or MPDL3280A In Combination with Carboplatin+ NAB-Pacilitaxel Versus Carboplatin+Paclitaxel in Chemotherapy-Naïve Patients with Stage IV Squamous Non-Small Cell Lung Cancer