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

content/public/browser/download_url_parameters.h

 // Copyright (c) 2012 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.
 
 #ifndef CONTENT_PUBLIC_BROWSER_DOWNLOAD_URL_PARAMETERS_H_
 #define CONTENT_PUBLIC_BROWSER_DOWNLOAD_URL_PARAMETERS_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 77 matching lines @@
   void set_callback(const OnStartedCallback& callback) {
     callback_ = callback;
   }
   void set_file_path(const base::FilePath& file_path) {
     save_info_.file_path = file_path;
   }
   void set_suggested_name(const base::string16& suggested_name) {
     save_info_.suggested_name = suggested_name;
   }
   void set_offset(int64 offset) { save_info_.offset = offset; }
-  void set_hash_state(std::string hash_state) {
+  void set_hash_state(const std::string& hash_state) {
     save_info_.hash_state = hash_state;
   }
   void set_prompt(bool prompt) { save_info_.prompt_for_save_location = prompt; }
   void set_file(base::File file) {
     save_info_.file = file.Pass();
   }
   void set_do_not_prompt_for_login(bool do_not_prompt) {
     do_not_prompt_for_login_ = do_not_prompt;
   }
 
@@ skipping 56 matching lines @@
   DownloadSaveInfo save_info_;
   GURL url_;
   bool do_not_prompt_for_login_;
 
   DISALLOW_COPY_AND_ASSIGN(DownloadUrlParameters);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_DOWNLOAD_URL_PARAMETERS_H_