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

net/dns/mdns_client_unittest.cc

Index: net/dns/mdns_client_unittest.cc
diff --git a/net/dns/mdns_client_unittest.cc b/net/dns/mdns_client_unittest.cc
index 7dccda12e5bbd32d54e18e976955db5246144ae6..bd84aca3d83469159640ac636e815731d19db322 100644
--- a/net/dns/mdns_client_unittest.cc
+++ b/net/dns/mdns_client_unittest.cc
@@ -412,7 +412,7 @@ class PtrRecordCopyContainer {
     ttl_ = value->ttl();
   }
 
-  bool IsRecordWith(std::string name, std::string ptrdomain) {
+  bool IsRecordWith(const std::string& name, const std::string& ptrdomain) {
     return set_ && name_ == name && ptrdomain_ == ptrdomain;
   }