Implemented ExternalData interface on DownloadItem and used it for SafeBrowsing.

chrome/browser/download/chrome_download_manager_delegate.h

Index: chrome/browser/download/chrome_download_manager_delegate.h
diff --git a/chrome/browser/download/chrome_download_manager_delegate.h b/chrome/browser/download/chrome_download_manager_delegate.h
index 284284ea95c2b51fd0edcff287e66dea0874b50e..b1f9e70bae6c2a1a6a71a2ba2de7d486d4607da1 100644
--- a/chrome/browser/download/chrome_download_manager_delegate.h
+++ b/chrome/browser/download/chrome_download_manager_delegate.h
@@ -145,16 +145,6 @@ class ChromeDownloadManagerDelegate
   typedef base::hash_map<CrxInstaller*, int> CrxInstallerMap;
   CrxInstallerMap crx_installers_;
 
-  // Maps the SafeBrowsing download check state to a DownloadItem ID.
-  struct SafeBrowsingState {
-    // If true the SafeBrowsing check is not done yet.
-    bool pending;
-    // The verdict that we got from calling CheckClientDownload.
-    safe_browsing::DownloadProtectionService::DownloadCheckResult verdict;
-  };
-  typedef base::hash_map<int, SafeBrowsingState> SafeBrowsingStateMap;
-  SafeBrowsingStateMap safe_browsing_state_;
-
   content::NotificationRegistrar registrar_;
 
   DISALLOW_COPY_AND_ASSIGN(ChromeDownloadManagerDelegate);