Persist offline page info in a navigation entry if needed

components/sessions/content/extended_info_handler.h

Index: components/sessions/content/extended_info_handler.h
diff --git a/components/sessions/content/extended_info_handler.h b/components/sessions/content/extended_info_handler.h
new file mode 100644
index 0000000000000000000000000000000000000000..d085c24301c39b5016cbb6859e7a518b0759731d
--- /dev/null
+++ b/components/sessions/content/extended_info_handler.h
@@ -0,0 +1,40 @@
+// 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:
+  virtual ~ExtendedInfoHandler() {}
+
+  // Returns the extended info from NavigationEntry for

[sky, 2016/09/29 03:08:19]

How about: "Returns the data to write to disk for the specified
NavigationEntry."

[jianli, 2016/09/29 22:02:29]

Done.

+  // SerializedNavigationEntry to save it.
+  virtual std::string GetExtendedInfo(
+      const content::NavigationEntry& entry) const = 0;
+
+  // Puts the extended info, extracted from SerializedNavigationEntry, into

[sky, 2016/09/29 03:08:19]

And similar to the above, "Restores |info| which was obtained from a previous
call to GetExtendedInfo() to a NavigationEntry.

[jianli, 2016/09/29 22:02:29]

Done.

+  // NavigationEntry.
+  virtual void RestoreExtendedInfo(
+      const std::string& info, content::NavigationEntry* entry) = 0;
+};
+
+}  // namespace sessions
+
+#endif  // COMPONENTS_SESSIONS_CONTENT_EXTENDED_INFO_HANDLER_H_