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

components/metrics/cloned_install_detector.h

Index: components/metrics/cloned_install_detector.h
diff --git a/components/metrics/cloned_install_detector.h b/components/metrics/cloned_install_detector.h
index 065cb490c507307d33cfaf320429a43ccf6e112f..3ff7558941a74b0cfe3d789f7fe9962da017afaa 100644
--- a/components/metrics/cloned_install_detector.h
+++ b/components/metrics/cloned_install_detector.h
@@ -46,7 +46,7 @@ class ClonedInstallDetector {
   // Converts raw_id into a 24-bit hash and stores the hash in |local_state|.
   // |raw_id| is not a const ref because it's passed from a cross-thread post
   // task.
-  void SaveMachineId(PrefService* local_state, std::string raw_id);
+  void SaveMachineId(PrefService* local_state, const std::string& raw_id);
 
   scoped_refptr<MachineIdProvider> raw_id_provider_;
   base::WeakPtrFactory<ClonedInstallDetector> weak_ptr_factory_;