Add the referrer url to the downloads table in the History database.

chrome/browser/history/download_database.h

Index: chrome/browser/history/download_database.h
diff --git a/chrome/browser/history/download_database.h b/chrome/browser/history/download_database.h
index afb5fd0a4642500f65cf838ab8735b30db121daf..ef85279ca0861115bc94b4a2bb98820f9dc8facf 100644
--- a/chrome/browser/history/download_database.h
+++ b/chrome/browser/history/download_database.h
@@ -67,6 +67,10 @@ class DownloadDatabase {
   // two target paths to downloads.
   bool MigrateDownloadsReasonPathsAndDangerType();
 
+  // Returns true if able to successfully add the referrer column to the
+  // downloads table.
+  bool MigrateReferrer();
+
   // Creates the downloads table if needed.
   bool InitDownloadTable();