Persist offline page info in a navigation entry if needed

components/sessions/content/extended_info_handler.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_SESSIONS_CONTENT_EXTENDED_INFO_HANDLER_H_
+#define COMPONENTS_SESSIONS_CONTENT_EXTENDED_INFO_HANDLER_H_
+
+#include <string>
+
+#include "components/sessions/core/sessions_export.h"
+
+namespace content {
+class NavigationEntry;
+}
+
+namespace sessions {
+
+// This interface is used to store and retrieve arbitrary key/value pairs for
+// a NavigationEntry that are not a core part of NavigationEntry.
+// WARNING: implementations must deal with versioning. In particular
+// RestoreExtendedInfo() may be called with data from a previous version of
+// Chrome.
+class SESSIONS_EXPORT ExtendedInfoHandler {
+ public:
+  ExtendedInfoHandler() {}
+  virtual ~ExtendedInfoHandler() {}
+
+  // Returns the data to write to disk for the specified NavigationEntry.
+  virtual std::string GetExtendedInfo(
+      const content::NavigationEntry& entry) const = 0;
+
+  // Restores |info| which was obtained from a previous call to
+  // GetExtendedInfo() to a NavigationEntry.
+  virtual void RestoreExtendedInfo(const std::string& info,
+                                   content::NavigationEntry* entry) = 0;
+};
+
+}  // namespace sessions
+
+#endif  // COMPONENTS_SESSIONS_CONTENT_EXTENDED_INFO_HANDLER_H_