Persist sessionStorage on disk.

content/public/browser/session_storage_namespace.h

 // Copyright (c) 2012 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 CONTENT_PUBLIC_BROWSER_SESSION_STORAGE_NAMESPACE_H_
 #define CONTENT_PUBLIC_BROWSER_SESSION_STORAGE_NAMESPACE_H_
 #pragma once
 
+#include <string>
+
 #include "base/memory/ref_counted.h"
 
 namespace content {
 
 // This is a ref-counted class that represents a SessionStorageNamespace.
 // On destruction it ensures that the storage namespace is destroyed.
 // NOTE: That if we're shutting down, we don't strictly need to do this, but
 //       it keeps valgrind happy.
 class SessionStorageNamespace
     : public base::RefCountedThreadSafe<SessionStorageNamespace> {
+ public:
+  virtual int64 id() const = 0;
+  virtual std::string persistent_id() const = 0;
  protected:
   friend class base::RefCountedThreadSafe<SessionStorageNamespace>;
   virtual ~SessionStorageNamespace() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_SESSION_STORAGE_NAMESPACE_H_