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

components/sync_driver/device_info.h

Index: components/sync_driver/device_info.h
diff --git a/components/sync_driver/device_info.h b/components/sync_driver/device_info.h
index d2a8f49a67b4e4669661d90c31063dceb1f218ab..a6c09557d513f4135111dbaf0829b8dac2ad02d8 100644
--- a/components/sync_driver/device_info.h
+++ b/components/sync_driver/device_info.h
@@ -68,7 +68,7 @@ class DeviceInfo {
   // not unique enough so the user can be tracked. Exposing |guid|
   // would lead to a stable unique id for a device which can potentially
   // be used for tracking.
-  void set_public_id(std::string id);
+  void set_public_id(const std::string& id);
 
   // Converts the |DeviceInfo| values to a JS friendly DictionaryValue,
   // which extension APIs can expose to third party apps.