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

net/udp/udp_socket_unittest.cc

Index: net/udp/udp_socket_unittest.cc
diff --git a/net/udp/udp_socket_unittest.cc b/net/udp/udp_socket_unittest.cc
index 57a8f5b79ad6e772f326645f463bb25b7e717c06..0a0a855425cbb73b2afe16ea7ac211501984d2ea 100644
--- a/net/udp/udp_socket_unittest.cc
+++ b/net/udp/udp_socket_unittest.cc
@@ -53,7 +53,7 @@ class UDPSocketTest : public PlatformTest {
   // If |address| is specified, then it is used for the destination
   // to send to. Otherwise, will send to the last socket this server
   // received from.
-  int SendToSocket(UDPServerSocket* socket, std::string msg) {
+  int SendToSocket(UDPServerSocket* socket, const std::string& msg) {
     return SendToSocket(socket, msg, recv_from_address_);
   }
 
@@ -94,7 +94,7 @@ class UDPSocketTest : public PlatformTest {
 
   // Loop until |msg| has been written to the socket or until an
   // error occurs.
-  int WriteSocket(UDPClientSocket* socket, std::string msg) {
+  int WriteSocket(UDPClientSocket* socket, const std::string& msg) {
     TestCompletionCallback callback;
 
     int length = msg.length();
@@ -116,12 +116,15 @@ class UDPSocketTest : public PlatformTest {
     return bytes_sent;
   }
 
-  void WriteSocketIgnoreResult(UDPClientSocket* socket, std::string msg) {
+  void WriteSocketIgnoreResult(UDPClientSocket* socket,
+                               const std::string& msg) {
     WriteSocket(socket, msg);
   }
 
   // Creates an address from ip address and port and writes it to |*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)