Fix GPUTestConfigTest.LoadCurrentConfig on macOS Sierra.

gpu/config/gpu_test_config.cc

Index: gpu/config/gpu_test_config.cc
diff --git a/gpu/config/gpu_test_config.cc b/gpu/config/gpu_test_config.cc
index 5f0c7ad2b0e12af179304d762f95dcf9a37fd698..8d5cb59f42d0f39bb7d40ccad17dcd9f7dceb4db 100644
--- a/gpu/config/gpu_test_config.cc
+++ b/gpu/config/gpu_test_config.cc
@@ -64,6 +64,8 @@ GPUTestConfig::OS GetCurrentOS() {
         return GPUTestConfig::kOsMacYosemite;
       case 11:
         return GPUTestConfig::kOsMacElCapitan;
+      case 12:
+        return GPUTestConfig::kOsMacSierra;
     }
   }
 #elif defined(OS_ANDROID)
@@ -189,6 +191,7 @@ bool GPUTestBotConfig::IsValid() const {
     case kOsMacMavericks:
     case kOsMacYosemite:
     case kOsMacElCapitan:
+    case kOsMacSierra:
     case kOsLinux:
     case kOsChromeOS:
     case kOsAndroid: