outer-element.html

<link rel="import" href="../polymer/polymer.html">
<link rel="import" href="seed-element.html">

<dom-module id="outer-element">
  <template>
    <seed-element id="seed" on-seed-element-lasers="underAttack"></seed-element>
  </template>

  <script>
    Polymer({
      is: 'outer-element',

      underAttack: function(e) {
        console.log("We're under fire!");
      },

      attached: function() {
          this.$.seed.fireLasers();
      }
    });
  </script>
</dom-module>