Cleanup: Pass std::string as const reference if possible

gpu/config/gpu_blacklist_unittest.cc

Index: gpu/config/gpu_blacklist_unittest.cc
diff --git a/gpu/config/gpu_blacklist_unittest.cc b/gpu/config/gpu_blacklist_unittest.cc
index 1a3deb6dc22fc8a4c40ff20881c6e40fa17d1323..1c7211e6d01f09d9580921198fcc54bd7695fbdf 100644
--- a/gpu/config/gpu_blacklist_unittest.cc
+++ b/gpu/config/gpu_blacklist_unittest.cc
@@ -23,8 +23,8 @@ class GpuBlacklistTest : public testing::Test {
     return gpu_info_;
   }
 
-  void RunFeatureTest(
-      const std::string feature_name, GpuFeatureType feature_type) {
+  void RunFeatureTest(const std::string& feature_name,
+                      GpuFeatureType feature_type) {
     const std::string json =
         "{\n"
         "  \"name\": \"gpu blacklist\",\n"