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

net/tools/flip_server/spdy_util.cc

 // Copyright (c) 2009 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/tools/flip_server/spdy_util.h"
 
 #include <string>
 
 #include "net/tools/flip_server/url_to_filename_encoder.h"
 
 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);
   }
 
   std::string filename;
   if (uri[0] == '/') {
     // uri is not fully qualified.
     filename = UrlToFilenameEncoder::Encode(
         "http://" + host + uri, method + "_/", false);
   } else {
     filename = UrlToFilenameEncoder::Encode(uri, method + "_/", false);
   }
   return filename;
 }
 
 }  // namespace net