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

net/udp/udp_socket_perftest.cc

Index: net/udp/udp_socket_perftest.cc
diff --git a/net/udp/udp_socket_perftest.cc b/net/udp/udp_socket_perftest.cc
index 00c6c70577e54f869114b8cbbd06e75740282062..6816c57cecbd695fa280166200274176715a97a7 100644
--- a/net/udp/udp_socket_perftest.cc
+++ b/net/udp/udp_socket_perftest.cc
@@ -52,7 +52,9 @@ class UDPSocketPerfTest : public PlatformTest {
 };
 
 // Creates and address from an ip/port and returns it in |address|.
-void CreateUDPAddress(std::string ip_str, uint16 port, IPEndPoint* address) {
+void CreateUDPAddress(const std::string& ip_str,
+                      uint16 port,
+                      IPEndPoint* address) {
   IPAddressNumber ip_number;
   bool rv = ParseIPLiteralToNumber(ip_str, &ip_number);
   if (!rv)