Cleanup: Pass std::string as const reference from content/

content/browser/renderer_host/p2p/socket_host_test_utils.cc

Index: content/browser/renderer_host/p2p/socket_host_test_utils.cc
diff --git a/content/browser/renderer_host/p2p/socket_host_test_utils.cc b/content/browser/renderer_host/p2p/socket_host_test_utils.cc
index ed0796649b25e9062b4af5f1c5309f392c756a40..cc37c0220829a2c70a4b3266be4365c668b942f4 100644
--- a/content/browser/renderer_host/p2p/socket_host_test_utils.cc
+++ b/content/browser/renderer_host/p2p/socket_host_test_utils.cc
@@ -208,7 +208,7 @@ void CreateStunError(std::vector<char>* packet) {
   CreateStunPacket(packet, kStunBindingError);
 }
 
-net::IPEndPoint ParseAddress(const std::string ip_str, uint16 port) {
+net::IPEndPoint ParseAddress(const std::string& ip_str, uint16 port) {
   net::IPAddressNumber ip;
   EXPECT_TRUE(net::ParseIPLiteralToNumber(ip_str, &ip));
   return net::IPEndPoint(ip, port);