Add new UMA stats to get a handle on Downloads UI Usage

chrome/browser/download/download_history.h

 // Copyright (c) 2011 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 CHROME_BROWSER_DOWNLOAD_DOWNLOAD_HISTORY_H_
 #define CHROME_BROWSER_DOWNLOAD_DOWNLOAD_HISTORY_H_
 #pragma once
 
 #include <map>
 
@@ skipping 34 matching lines @@
   void AddEntry(DownloadItem* download_item,
                 HistoryService::DownloadCreateCallback* callback);
 
   // Updates the history entry for |download_item|.
   void UpdateEntry(DownloadItem* download_item);
 
   // Updates the download path for |download_item| to |new_path|.
   void UpdateDownloadPath(DownloadItem* download_item,
                           const FilePath& new_path);
 
+  void MarkDownloadOpened(int64 db_handle);
+
   // Removes |download_item| from the history database.
   void RemoveEntry(DownloadItem* download_item);
 
   // Removes download-related history entries in the given time range.
   void RemoveEntriesBetween(const base::Time remove_begin,
                             const base::Time remove_end);
 
   // Returns a new unique database handle which will not collide with real ones.
   int64 GetNextFakeDbHandle();
 
@@ skipping 17 matching lines @@
 
   CancelableRequestConsumer history_consumer_;
 
   // The outstanding requests made by CheckVisitedReferrerBefore().
   VisitedBeforeRequestsMap visited_before_requests_;
 
   DISALLOW_COPY_AND_ASSIGN(DownloadHistory);
 };
 
 #endif  // CHROME_BROWSER_DOWNLOAD_DOWNLOAD_HISTORY_H_