How do I toggle a legend of a cartodb layer in a leaflet map?

Per my previous question - here - how do I get the legend to toggle (I have it turned off now) in conjunction with toggling the cartodb layer via the leaflet layer control? Maybe adding it as a variable some way?

  var cdb_url = 'http://ift.tt/1wYrS4v';
  cartodb.createLayer(map, cdb_url, {legends:false})
    .addTo(map)
    .on('done', function(crashes) {
      crashes.setZIndex(2);
      var overlayMaps = {
        "Vehicle Crashes": crashes
      };
      L.control.layers(baseMaps, overlayMaps, {collapsed: false}).addTo(map);
    })
    .on('error', function(err) {
      alert("some error occurred: " + err);
    });