The CEF is directly integrated now with the X-Plane 12 application. In the past X-Plane 11 would create an instance of CEF when a sim session would start however if a plug-in utilizes CEF before the XPlane 11 instance starts then the plug-in owns and controls CEF. The change between XPlane 11 and 12 is now CEF is directly managed and ran with the application and you can interface with it instead of having to run another CEF instance.

I'm not 100% positive but I belive you need to call any CEF interaction through the XPlane 12 API. Currently investigating this myself as I'm working on the AeroGenesis A330 project.