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

components/ntp_snippets/offline_pages/recent_tab_suggestions_provider.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/offline_pages/recent_tab_suggestions_provider.h"
 
 #include <algorithm>
 #include <utility>
 
 #include "base/bind.h"
@@ skipping 239 matching lines @@
     // TODO(vitaliii): Remove this fallback once the OfflinePageModel provides
     // titles for all (relevant) OfflinePageItems.
     suggestion.set_title(base::UTF8ToUTF16(offline_page.url.spec()));
   } else {
     suggestion.set_title(offline_page.title);
   }
   suggestion.set_publish_date(offline_page.creation_time);
   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;
 }
 
 std::vector<ContentSuggestion>
 RecentTabSuggestionsProvider::GetMostRecentlyVisited(
     std::vector<const OfflinePageItem*> offline_page_items) const {
   std::sort(offline_page_items.begin(), offline_page_items.end(),
             OrderOfflinePagesByMostRecentlyVisitedFirst());
   std::vector<ContentSuggestion> suggestions;
@@ skipping 25 matching lines @@
 }
 
 void RecentTabSuggestionsProvider::StoreDismissedIDsToPrefs(
     const std::set<std::string>& dismissed_ids) {
   prefs::StoreDismissedIDsToPrefs(pref_service_,
                                   prefs::kDismissedRecentOfflineTabSuggestions,
                                   dismissed_ids);
 }
 
 }  // namespace ntp_snippets