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

components/ntp_snippets/content_suggestion.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/ntp_snippets/content_suggestion.h"
 
 #include <utility>
 
 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_;
 }
 
 bool ContentSuggestion::ID::operator!=(const ID& rhs) const {
   return !(*this == rhs);
 }
 
 ContentSuggestion::ContentSuggestion(const ID& id, const GURL& url)
@@ skipping 21 matching lines @@
   download_suggestion_extra_ = std::move(download_suggestion_extra);
 }
 
 void ContentSuggestion::set_recent_tab_suggestion_extra(
     std::unique_ptr<RecentTabSuggestionExtra> recent_tab_suggestion_extra) {
   DCHECK(id_.category().IsKnownCategory(KnownCategories::RECENT_TABS));
   recent_tab_suggestion_extra_ = std::move(recent_tab_suggestion_extra);
 }
 
 }  // namespace ntp_snippets