title: Manually recalculate 'computed properties'
body: <p>If I have a custom element</p>
  
  <pre><code>Polymer({
    name: 'dane',
  
    computed: {
      message: 'greet(name)'
    },
  
    greet: function(name) {
      return 'hello ' + name + Date.now();
    }
  })
  </code></pre>
  
  <p>When I change <code>name</code> polymer will automatically recompute <code>message</code>, but is there a way to recompute <code>message</code> without changing <code>name</code>?</p>