Don't use the private class, what made you think you can use the private class? it's *private* so obviously it's non usable (unless you know what you're doing and you have reasons for it).
I already told you on IRC how to fix it a long time ago, if you need the functionality, just make it accessible in Page.
By the way does this mean you haven't tested this code at all to see if it actually does anything at all?
This change is totally unacceptable.
Sometimes I think it makes sense to move the context menu to the widget it belongs to. That widget would accept the context menu event, and create a context menu. Basically the same context menu that is currently created by Part.
Because PageView will create the context menu then, it should be possible to access Page correctly.
Just a thought...