Abstract content::SessionStorageNamespace from core TabRestore code

components/sessions/content/content_tab_client_data.h

Index: components/sessions/content/content_tab_client_data.h
diff --git a/components/sessions/content/content_tab_client_data.h b/components/sessions/content/content_tab_client_data.h
new file mode 100644
index 0000000000000000000000000000000000000000..311e56bd61cfaaef528235a72421f799d705debd
--- /dev/null
+++ b/components/sessions/content/content_tab_client_data.h
@@ -0,0 +1,35 @@
+// Copyright 2015 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_CONTENT_CLIENT_DATA_H_
+#define COMPONENTS_SESSIONS_CONTENT_CONTENT_CLIENT_DATA_H_
+
+#include "base/memory/ref_counted.h"
+#include "components/sessions/core/tab_restore_service_client.h"
+#include "components/sessions/sessions_export.h"
+#include "content/public/browser/session_storage_namespace.h"
+
+namespace sessions {
+
+// A //content-specific subclass of TabClientData that is used to associate
+// TabRestoreService::Tab instances with the content::SessionStorageNamespace
+// of the WebContents from which they were created.
+class SESSIONS_EXPORT ContentTabClientData : public TabClientData {
+ public:
+  explicit ContentTabClientData(content::WebContents* web_contents);
+
+  content::SessionStorageNamespace* session_storage_namespace() const {
+    return session_storage_namespace_.get();
+  }
+
+ private:
+  friend class base::RefCountedThreadSafe<ContentTabClientData>;
+  ~ContentTabClientData() override;
+
+  scoped_refptr<content::SessionStorageNamespace> session_storage_namespace_;
+};
+
+}  // namespace sessions
+
+#endif  // COMPONENTS_SESSIONS_CONTENT_CONTENT_CLIENT_DATA_H_