title: Forcing Polymer expression re-evaluation on filter change
body: <p>I am trying to add a filter which return value depends on some private static variable value of my component. Is there a way to re-evaluate expressions using this filter on change of this variable?</p>
  
  <p>For example:</p>
  
  <pre><code>{{ someVariable | myFilter }}
  </code></pre>
  
  <p>where <code>myFilter</code> depends on a value of some private variable. Right now it evaluates only once.</p>