title: Listening children's property change notifier using prototype's listeners property in Polymer not working
body: <p>Why will not this work ?
  I am trying to use <code>notify</code> and <code>listeners</code> together. Am I missing something ?</p>
  
  <pre><code>Polymer({
    is: 'x-child',
  
    properties: {
      message: {
        type: String,
        value: '',
        notify: true
      }
    }
  });
  
  Polymer({
    is: 'x-dad',
  
    listeners: {
      'message-changed': '_onMessageReceived'
    },
  
    _onMessageReceived: function (e) {
      alert('child sent a message');
    }
  });
  </code></pre>
  
  <p><strong>scenario</strong></p>
  
  <pre><code>var d = document.createElement('x-dad');
  var c = document.createElement('x-child');
  d.appendChild(c);
  c.message = 'new';
  </code></pre>