Rewrite std::string("") to std::string(), Linux edition.

net/server/http_server_request_info.cc

 // Copyright (c) 2011 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/server/http_server_request_info.h"
 
 namespace net {
 
 HttpServerRequestInfo::HttpServerRequestInfo() {}
 
 HttpServerRequestInfo::~HttpServerRequestInfo() {}
 
 std::string HttpServerRequestInfo::GetHeaderValue(
     const std::string& header_name) const {
   HttpServerRequestInfo::HeadersMap::const_iterator it =
       headers.find(header_name);
   if (it != headers.end())
     return it->second;
-  return "";
+  return std::string();
 }
 
 }  // namespace net