Communicating between Lightning component and VF Page

Finallyyyyyyyy I figured out !!!

I had set development mode on in my user profile**** because of which I was getting the following error.

Uncaught DOMException: Blocked a frame with origin "" from accessing a cross-origin frame. at EditAreaLoader.add_event

As soon as I deactivated the development mode and lost access to the VF code editor, the window.postmessage was successfully posting as expected.