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

chrome/browser/ntp_snippets/download_suggestions_provider.cc

Index: chrome/browser/ntp_snippets/download_suggestions_provider.cc
diff --git a/chrome/browser/ntp_snippets/download_suggestions_provider.cc b/chrome/browser/ntp_snippets/download_suggestions_provider.cc
index c5ef7dda97185091978abecbf1b093c809bb452e..332dfeb93bc242d2da83b31f3630949f365b95b0 100644
--- a/chrome/browser/ntp_snippets/download_suggestions_provider.cc
+++ b/chrome/browser/ntp_snippets/download_suggestions_provider.cc
@@ -488,6 +488,7 @@ ContentSuggestion DownloadSuggestionsProvider::ConvertOfflinePage(
   suggestion.set_publisher_name(base::UTF8ToUTF16(offline_page.url.host()));
   auto extra = base::MakeUnique<ntp_snippets::DownloadSuggestionExtra>();
   extra->is_download_asset = false;
+  extra->offline_page_id = base::Int64ToString(offline_page.offline_id);
   suggestion.set_download_suggestion_extra(std::move(extra));
   return suggestion;
 }