[Downloads] Introduce GUIDs for downloads.

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 121 matching lines @@
 
   // Allow objects to observe the download creation process.
   virtual void AddObserver(Observer* observer) = 0;
 
   // Remove a download observer from ourself.
   virtual void RemoveObserver(Observer* observer) = 0;
 
   // Called by the embedder, after creating the download manager, to let it know
   // about downloads from previous runs of the browser.
   virtual DownloadItem* CreateDownloadItem(
+      const std::string& guid,
       uint32_t id,
       const base::FilePath& current_path,
       const base::FilePath& target_path,
       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,
@@ skipping 18 matching lines @@
 
   virtual BrowserContext* GetBrowserContext() const = 0;
 
   // Checks whether downloaded files still exist. Updates state of downloads
   // that refer to removed files. The check runs in the background and may
   // finish asynchronously after this method returns.
   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.
+  // DEPRECATED: Don't add new callers for GetDownload(uint32_t). Instead keep
+  // track of the GUID and use GetDownloadByGuid(), or observe the DownloadItem
+  // if you need to keep track of a specific download. (http://crbug.com/593020)
   virtual DownloadItem* GetDownload(uint32_t id) = 0;
+
+  // Get the download item for |guid|.
+  virtual DownloadItem* GetDownloadByGuid(const std::string& guid) = 0;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_DOWNLOAD_MANAGER_H_