Make DownloadItem derive SupportsUserData instead of re-implementing it.

content/browser/download/download_item_impl.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_BROWSER_DOWNLOAD_DOWNLOAD_ITEM_IMPL_H_
 #define CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_ITEM_IMPL_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 177 matching lines @@
   virtual content::DownloadInterruptReason GetLastReason() const OVERRIDE;
   virtual content::DownloadPersistentStoreInfo
       GetPersistentStoreInfo() const OVERRIDE;
   virtual content::BrowserContext* GetBrowserContext() const OVERRIDE;
   virtual content::WebContents* GetWebContents() const OVERRIDE;
   virtual FilePath GetFileNameToReportUser() const OVERRIDE;
   virtual void SetDisplayName(const FilePath& name) OVERRIDE;
   virtual FilePath GetUserVerifiedFilePath() const OVERRIDE;
   virtual std::string DebugString(bool verbose) const OVERRIDE;
   virtual void MockDownloadOpenForTesting() OVERRIDE;
-  virtual ExternalData* GetExternalData(const void* key) OVERRIDE;
-  virtual const ExternalData* GetExternalData(const void* key) const OVERRIDE;
-  virtual void SetExternalData(const void* key, ExternalData* data) OVERRIDE;
 
  private:
   // Construction common to all constructors. |active| should be true for new
   // downloads and false for downloads from the history.
   // |download_type| indicates to the net log system what kind of download
   // this is.
   void Init(bool active, download_net_logs::DownloadType download_type);
 
   // Returns true if the download still needs to be renamed to
   // GetTargetFilePath().
@@ skipping 186 matching lines @@
   // when the user closes the shelf before the item has been opened but should
   // be treated as though the user opened it.
   bool opened_;
 
   // Do we actually open downloads when requested?  For testing purposes only.
   bool open_enabled_;
 
   // Did the delegate delay calling Complete on this download?
   bool delegate_delayed_complete_;
 
-  // External Data storage.  All objects in the store
-  // are owned by the DownloadItemImpl.
-  std::map<const void*, ExternalData*> external_data_map_;
-
   // Net log to use for this download.
   const net::BoundNetLog bound_net_log_;
 
   base::WeakPtrFactory<DownloadItemImpl> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(DownloadItemImpl);
 };
 
 #endif  // CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_ITEM_IMPL_H_