Downloads: Added transient flag to download item and download database

chrome/browser/ntp_snippets/fake_download_item.cc

Index: chrome/browser/ntp_snippets/fake_download_item.cc
diff --git a/chrome/browser/ntp_snippets/fake_download_item.cc b/chrome/browser/ntp_snippets/fake_download_item.cc
index 6a1ebffa9dfdd79346355996abb27d419587e047..4d9d7d2218c637bdd9f8c07148d6089e67bf1017 100644
--- a/chrome/browser/ntp_snippets/fake_download_item.cc
+++ b/chrome/browser/ntp_snippets/fake_download_item.cc
@@ -368,6 +368,11 @@ base::Time FakeDownloadItem::GetLastAccessTime() const {
   return base::Time();
 }
 
+bool FakeDownloadItem::IsVisible() const {
+  NOTREACHED();
+  return true;
+}
+
 content::BrowserContext* FakeDownloadItem::GetBrowserContext() const {
   NOTREACHED();
   return nullptr;