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

net/tools/flip_server/spdy_util.cc

Index: net/tools/flip_server/spdy_util.cc
diff --git a/net/tools/flip_server/spdy_util.cc b/net/tools/flip_server/spdy_util.cc
index a8cbd683dcdc577369c347fd7529abfeaf6f112d..34b6072cfa85acb82be0e9d28d7ab4b9c5076312 100644
--- a/net/tools/flip_server/spdy_util.cc
+++ b/net/tools/flip_server/spdy_util.cc
@@ -13,7 +13,9 @@ namespace net {
 bool g_need_to_encode_url = false;
 
 // Encode the URL.
-std::string EncodeURL(std::string uri, std::string host, std::string method) {
+std::string EncodeURL(const std::string& uri,
+                      const std::string& host,
+                      const std::string& method) {
   if (!g_need_to_encode_url) {
     // TODO(mbelshe): if uri is fully qualified, need to strip protocol/host.
     return std::string(method + "_" + uri);