experiment with -Wimplicit-fallthrough

gpu/config/gpu_info_collector_mac.mm

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "gpu/config/gpu_info_collector.h"
 
 #include <vector>
 
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
@@ skipping 108 matching lines @@
           }
         }
         if (integrated >= 0 && discrete >= 0) {
           // We always put discrete GPU as primary for blacklisting purpose.
           gpu_info->gpu = gpu_list[discrete];
           gpu_info->secondary_gpus.push_back(gpu_list[integrated]);
           break;
         }
         // If it's not optimus or amd_switchable, we put the current GPU as
         // primary.  Fall through to default.
+        FALLTHROUGH_INTENDED;
       }
     default:
       {
         GPUInfo::GPUDevice active_gpu = GetActiveGPU();
         size_t current = gpu_list.size();
         if (active_gpu.vendor_id && active_gpu.device_id) {
           for (size_t i = 0; i < gpu_list.size(); ++i) {
             if (gpu_list[i].vendor_id == active_gpu.vendor_id &&
                 gpu_list[i].device_id == active_gpu.device_id) {
               current = i;
@@ skipping 72 matching lines @@
   gpu_info->driver_version = gl_version_string.substr(pos + 1);
   return true;
 }
 
 void MergeGPUInfo(GPUInfo* basic_gpu_info,
                   const GPUInfo& context_gpu_info) {
   MergeGPUInfoGL(basic_gpu_info, context_gpu_info);
 }
 
 }  // namespace gpu