Hi Dmitry Lomov,
From the comment https://bugs.webkit.org/show_bug.cgi?id=66789#c4
"It also seems to me we could change things so a MessageEvent always has a MessagePortArray in it, and then we might not need a custom binding at all!"
I am cleaning up custom bindings code for the attributes of type Array. MessageEvent.idl is also in this list.
But first I think we should make change MessageEvent to have a MessagePortArray in it. Can you please provide feedback on this.