Persist offline page info in a navigation entry if needed

components/sessions/core/serialized_navigation_entry.h

Index: components/sessions/core/serialized_navigation_entry.h
diff --git a/components/sessions/core/serialized_navigation_entry.h b/components/sessions/core/serialized_navigation_entry.h
index cc3b53d0f29df4d1cca140c959c8aa9b0c3f112e..947414f0cdf8dbd0a8a1c9898b0207f9d2473728 100644
--- a/components/sessions/core/serialized_navigation_entry.h
+++ b/components/sessions/core/serialized_navigation_entry.h
@@ -122,6 +122,7 @@ class SESSIONS_EXPORT SerializedNavigationEntry {
     content_pack_categories_ = content_pack_categories;
   }
   const std::vector<GURL>& redirect_chain() const { return redirect_chain_; }
+  const std::string& offline_page_info() const { return offline_page_info_; }
 
  private:
   friend class ContentSerializedNavigationBuilder;
@@ -151,6 +152,7 @@ class SESSIONS_EXPORT SerializedNavigationEntry {
   int http_status_code_;
   bool is_restored_;    // Not persisted.
   std::vector<GURL> redirect_chain_;  // Not persisted.
+  std::string offline_page_info_;  // Not synced.
 
   // Additional information.
   BlockedState blocked_state_;