[remote suggestions] Attach the fetch time to RemoteSnippets, ContentSnippets and SnippetArticle

components/ntp_snippets/content_suggestion.h

 // 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.
 
 #ifndef COMPONENTS_NTP_SNIPPETS_CONTENT_SUGGESTION_H_
 #define COMPONENTS_NTP_SNIPPETS_CONTENT_SUGGESTION_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 133 matching lines @@
   // Extra information for notifications. When absent, no notification should be
   // sent for this suggestion. When present, a notification should be sent,
   // unless other factors disallow it (examples: the extra parameters say to;
   // notifications are disabled; Chrome is in the foreground).
   NotificationExtra* notification_extra() const {
     return notification_extra_.get();
   }
   void set_notification_extra(
       std::unique_ptr<NotificationExtra> notification_extra);
 
+  const base::Time& fetch_date() const { return fetch_date_; }
+  void set_fetch_date(const base::Time& fetch_date) {
+    fetch_date_ = fetch_date;
+  }
+
  private:
   ID id_;
   GURL url_;
   base::string16 title_;
   base::string16 snippet_text_;
   base::Time publish_date_;
   base::string16 publisher_name_;
   float score_;
   std::unique_ptr<DownloadSuggestionExtra> download_suggestion_extra_;
   std::unique_ptr<RecentTabSuggestionExtra> recent_tab_suggestion_extra_;
   std::unique_ptr<NotificationExtra> notification_extra_;
 
+  // The time when the remote suggestion was fetched from the server. This field
+  // is only populated when the ContentSuggestion is created from a
+  // RemoteSuggestion.
+  base::Time fetch_date_;
+
   DISALLOW_COPY_AND_ASSIGN(ContentSuggestion);
 };
 
 std::ostream& operator<<(std::ostream& os, const ContentSuggestion::ID& id);
 
 }  // namespace ntp_snippets
 
 #endif  // COMPONENTS_NTP_SNIPPETS_CONTENT_SUGGESTION_H_