Persist sessionStorage on disk.

content/browser/dom_storage/session_storage_namespace_impl.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_BROWSER_DOM_STORAGE_SESSION_STORAGE_NAMESPACE_IMPL_H_
 #define CONTENT_BROWSER_DOM_STORAGE_SESSION_STORAGE_NAMESPACE_IMPL_H_
 #pragma once
 
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
 #include "content/common/content_export.h"
 #include "content/public/browser/session_storage_namespace.h"
 
 class DOMStorageContextImpl;
 
 namespace dom_storage {
 class DomStorageSession;
 }
 
 class SessionStorageNamespaceImpl
     : NON_EXPORTED_BASE(public content::SessionStorageNamespace) {
  public:
   explicit SessionStorageNamespaceImpl(DOMStorageContextImpl* context);
   SessionStorageNamespaceImpl(DOMStorageContextImpl* context,
                               int64 namepace_id_to_clone);
-  int64 id() const;
+  SessionStorageNamespaceImpl(DOMStorageContextImpl* context,
+                              const std::string& persistent_id);
+  virtual int64 id() const OVERRIDE;
+  virtual std::string persistent_id() const OVERRIDE;
   SessionStorageNamespaceImpl* Clone();
 
  private:
   explicit SessionStorageNamespaceImpl(dom_storage::DomStorageSession* clone);
   virtual ~SessionStorageNamespaceImpl();
 
   scoped_refptr<dom_storage::DomStorageSession> session_;
 
   DISALLOW_COPY_AND_ASSIGN(SessionStorageNamespaceImpl);
 };
 
 #endif  // CONTENT_BROWSER_DOM_STORAGE_SESSION_STORAGE_NAMESPACE_IMPL_H_