Cleanup parameter passing issues in content/browser/download

content/public/browser/download_manager.h

 // 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.
 //
 // The DownloadManager object manages the process of downloading, including
 // updates to the history system and providing the information for displaying
 // the downloads view in the Destinations tab. There is one DownloadManager per
 // active browser context in Chrome.
 //
 // Download observers:
@@ skipping 90 matching lines @@
                                DownloadVector* result) = 0;
 
   // Returns true if initialized properly.
   virtual bool Init(content::BrowserContext* browser_context) = 0;
 
   // Notifications sent from the download thread to the UI thread
   virtual void StartDownload(int32 id) = 0;
   virtual void UpdateDownload(int32 download_id,
                               int64 bytes_so_far,
                               int64 bytes_per_sec,
-                              std::string hash_state) = 0;
+                              const std::string& hash_state) = 0;
 
   // |download_id| is the ID of the download.
   // |size| is the number of bytes that have been downloaded.
   // |hash| is sha256 hash for the downloaded file. It is empty when the hash
   // is not available.
   virtual void OnResponseCompleted(int32 download_id, int64 size,
                            const std::string& hash) = 0;
 
   // Offthread target for cancelling a particular download.  Will be a no-op
   // if the download has already been cancelled.
   virtual void CancelDownload(int32 download_id) = 0;
 
   // Called when there is an error in the download.
   // |download_id| is the ID of the download.
   // |size| is the number of bytes that are currently downloaded.
   // |hash_state| is the current state of the hash of the data that has been
   // downloaded.
   // |reason| is a download interrupt reason code.
   virtual void OnDownloadInterrupted(int32 download_id,
                                      int64 size,
-                                     std::string hash_state,
+                                     const std::string& hash_state,
                                      InterruptReason reason) = 0;
 
   // Called when the download is renamed to its final name.
   // |uniquifier| is a number used to make unique names for the file.  It is
   // only valid for the DANGEROUS_BUT_VALIDATED state of the download item.
   virtual void OnDownloadRenamedToFinalName(int download_id,
                                     const FilePath& full_path,
                                     int uniquifier) = 0;
 
   // Remove downloads after remove_begin (inclusive) and before remove_end
@@ skipping 119 matching lines @@
   friend class base::RefCountedThreadSafe<
       DownloadManager, content::BrowserThread::DeleteOnUIThread>;
   friend struct content::BrowserThread::DeleteOnThread<
       content::BrowserThread::UI>;
   friend class DeleteTask<DownloadManager>;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_DOWNLOAD_MANAGER_H_