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

components/sync_driver/device_info.cc

Index: components/sync_driver/device_info.cc
diff --git a/components/sync_driver/device_info.cc b/components/sync_driver/device_info.cc
index c80a1571c964640a6c00ea74fe10939a90f6275c..b645ca9f433ffd83ae179150e8747dfa6b24b1c3 100644
--- a/components/sync_driver/device_info.cc
+++ b/components/sync_driver/device_info.cc
@@ -106,7 +106,7 @@ base::DictionaryValue* DeviceInfo::ToValue() {
   return value;
 }
 
-void DeviceInfo::set_public_id(std::string id) {
+void DeviceInfo::set_public_id(const std::string& id) {
   public_id_ = id;
 }