Downloads: Added transient flag to download item and download database

content/public/browser/download_item.h

Index: content/public/browser/download_item.h
diff --git a/content/public/browser/download_item.h b/content/public/browser/download_item.h
index 80e0c63cd53514b922698a4faf3d08964a7cba58..9c5c4fa7bb46d9e578b21423ce6c0d43d5c27d85 100644
--- a/content/public/browser/download_item.h
+++ b/content/public/browser/download_item.h
@@ -400,6 +400,9 @@ class CONTENT_EXPORT DownloadItem : public base::SupportsUserData {
   // been opened.
   virtual base::Time GetLastAccessTime() const = 0;
 
+  // Returns whether the download item should be visible in the UI.
+  virtual bool IsVisible() const = 0;
+
   //    Misc State accessors ---------------------------------------------------
 
   // BrowserContext that indirectly owns this download. Always valid.