UploadExPage class

Hello:

I am trying to inherit UploadExPage class but unable to find the class from any of the assemblies/namespaces.

I added following assemblies: Microsoft.Office.Policy and Microsoft.SharePoint. When I look into UploadEx.aspx at 15\TEMPLATE\LAYOUTS, I can see that they have a reference to "Microsoft.Office.RecordsManagement.PolicyFeatures.ApplicationPages.UploadExPage" but I am unable to find it.

Does anyone know which assembly I need to reference? Or do you think it's a sealed class that I cannot inherit anymore? We used to be able to inherit in SharePoint 2010.

Any pointers?