[NTP] Propagate OfflineId from C++ for Downloads.

components/ntp_snippets/offline_pages/recent_tab_suggestions_provider.cc

Index: components/ntp_snippets/offline_pages/recent_tab_suggestions_provider.cc
diff --git a/components/ntp_snippets/offline_pages/recent_tab_suggestions_provider.cc b/components/ntp_snippets/offline_pages/recent_tab_suggestions_provider.cc
index 2a135b1b2a387155b9b61f4af1464ddc1fd17509..eea6875456b3364b5d4462a760b5f113fccb0d08 100644
--- a/components/ntp_snippets/offline_pages/recent_tab_suggestions_provider.cc
+++ b/components/ntp_snippets/offline_pages/recent_tab_suggestions_provider.cc
@@ -257,7 +257,7 @@ ContentSuggestion RecentTabSuggestionsProvider::ConvertOfflinePage(
   suggestion.set_publisher_name(base::UTF8ToUTF16(offline_page.url.host()));
   auto extra = base::MakeUnique<RecentTabSuggestionExtra>();
   extra->tab_id = offline_page.client_id.id;
-  extra->offline_page_id = base::Int64ToString(offline_page.offline_id);
+  extra->offline_page_id = offline_page.offline_id;
   suggestion.set_recent_tab_suggestion_extra(std::move(extra));
   return suggestion;
 }