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

components/ntp_snippets/content_suggestion.cc

Index: components/ntp_snippets/content_suggestion.cc
diff --git a/components/ntp_snippets/content_suggestion.cc b/components/ntp_snippets/content_suggestion.cc
index efe1aad967e5adbc998d7d44fda191682068091c..a1a1d4e8007139dcdf5a7e5d67dad38d47a957de 100644
--- a/components/ntp_snippets/content_suggestion.cc
+++ b/components/ntp_snippets/content_suggestion.cc
@@ -8,6 +8,10 @@
 
 namespace ntp_snippets {
 
+DownloadSuggestionExtra::DownloadSuggestionExtra() = default;
+
+DownloadSuggestionExtra::~DownloadSuggestionExtra() = default;
+
 bool ContentSuggestion::ID::operator==(const ID& rhs) const {
   return category_ == rhs.category_ &&
          id_within_category_ == rhs.id_within_category_;