Use a LocalSocket to represent the connection between two message ports.
The concept of the port message queue is still missing, however. When
that concept is implemented, the "steps" in step 7 of the message port
transfer steps will need to send the serialized data over the connected
socketpair and run in the event loop of the process that holds onto the
other side of the message port. Doing this should allow centralizing the
behavior of postMessage for Window, MessagePorts and Workers.
