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 48309b60b1e39503fb01a663c43c69b7500c7a7e..0b712396e339b27be422f4dc5891d66036bc72f7 100644
--- a/content/public/browser/download_item.h
+++ b/content/public/browser/download_item.h
@@ -402,6 +402,10 @@ class CONTENT_EXPORT DownloadItem : public base::SupportsUserData {
   // been opened.
   virtual base::Time GetLastAccessTime() const = 0;
 
+  // Returns whether the download item is transient. Transient items are cleaned
+  // up after completion and not shown in the UI.
+  virtual bool IsTransient() const = 0;
+
   //    Misc State accessors ---------------------------------------------------
 
   // BrowserContext that indirectly owns this download. Always valid.