[Downloads] Rework how hashes are calculated for download files.

content/public/browser/download_manager.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.
 //
 // 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 134 matching lines @@
       const std::vector<GURL>& url_chain,
       const GURL& referrer_url,
       const std::string& mime_type,
       const std::string& original_mime_type,
       const base::Time& start_time,
       const base::Time& end_time,
       const std::string& etag,
       const std::string& last_modified,
       int64_t received_bytes,
       int64_t total_bytes,
+      const std::string& hash,
       DownloadItem::DownloadState state,
       DownloadDangerType danger_type,
       DownloadInterruptReason interrupt_reason,
       bool opened) = 0;
 
   // The number of in progress (including paused) downloads.
   // Performance note: this loops over all items. If profiling finds that this
   // is too slow, use an AllDownloadItemNotifier to count in-progress items.
   virtual int InProgressCount() const = 0;
 
@@ skipping 11 matching lines @@
   virtual void CheckForHistoryFilesRemoval() = 0;
 
   // Get the download item for |id| if present, no matter what type of download
   // it is or state it's in.
   virtual DownloadItem* GetDownload(uint32_t id) = 0;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_DOWNLOAD_MANAGER_H_