Downsides with this proposal:
* There is no way to communicate back unless first communicated to.
* The first one to instantiate a shared worker get special treatment.
=== Proposal 2 ===
The <code>Worker</code> receives the other <code>MessagePort</code> through an <code>onconnect</code> <code>Event</code> fired on the <code>WorkerGlobalScope</code> object.
* There is no way to get a reference to the shared <code>Worker</code> object itself.
* Communication for shared workers is different from communication for non-shared ones.