Timing of MessagePort entanglement transfer

[karlt]

Consider:

const mc = new MessageChannel;
const shipper = new MessageChannel;
shipper.port1.postMessage(null, [mc.port1]);
shipper.port1.postMessage(null, [mc.port2]);
let i = 0;
shipper.port2.onmessage = ({ports: [shipped]}) => {
  ++i;
  shipped.onmessage = e => console.log(e.data);
  shipped.postMessage(`message ${i}`);
};

I'd expect 'message 1' and 'message 2' to be logged. That's what happens in Firefox and Chrome, but that's not what the spec says.

IIUC the spec says the task for 'message 1' will be put in the port message queue of mc.port2 and then moved to the port message queue of the corresponding shipped port (in transfer-receiving steps) and logged. However, the task for 'message 2' will be put in the port message queue of mc.port1 and is not moved to another port message queue.

@gterzian