Downloads: Added transient flag to download item and download database

components/history/core/browser/download_row.h

Index: components/history/core/browser/download_row.h
diff --git a/components/history/core/browser/download_row.h b/components/history/core/browser/download_row.h
index 9c0539748757b1e361ae451e8509639de0623a4f..c72c90320931d8f037373fe3c3ec22b08dcc9df0 100644
--- a/components/history/core/browser/download_row.h
+++ b/components/history/core/browser/download_row.h
@@ -47,6 +47,7 @@ struct DownloadRow {
               const std::string& guid,
               bool download_opened,
               const base::Time& last_access,
+              bool visible,
               const std::string& ext_id,
               const std::string& ext_name,
               const std::vector<DownloadSliceInfo>& download_slice_info);
@@ -138,6 +139,9 @@ struct DownloadRow {
   // The time when the download was last accessed.
   base::Time last_access_time;
 
+  // Whether this download is visible.
+  bool visible;
+
   // The id and name of the extension that created this download.
   std::string by_ext_id;
   std::string by_ext_name;