"On Before Upload dialog" type events?

[HarmlessDave]

A search on "upload" in the CEFClient, etc. source only turns up the upload progress events. Is there any way to other than injecting site-specific JavaScript to let C++ code decide whether or not to allow showing the choose file dialog? Or is that something that Chromium does not expose at all?

Our use case is similar to navigation blocking, except we only want to allow file uploads for certain "safe" web pages when we still allow navigating to other pages that include file upload options.