The asymmetry between this and the `_commandHandler` above seems a little strange to me. To receive commands, we listen for a DOM event, but to send updates, we call a method on this object. On my branch, I added a method called `addEventListener` to `MediaRemoteControls.prototype`, which lets me do something like so:

```
myRemoteControls.addEventListener('play', function(event) {
  /* Do something to make playback start here. */
});