title: Make custom overlay clickable (Google Maps API v3)
body: <p>I have a custom overlay class (<code>ImageOverlay</code>) which inherits from <code>google.maps.OverlayView</code>. I want it to respond to Google Maps click events (not just DOM click events) but simply using <code>addListener</code> doesn't seem to do the trick. </p>
  
  <p>e.g. I have a <code>shapes</code> array which contains a mixture of <code>google.maps.Polygon</code> and <code>ImageOverlay</code> objects:</p>
  
  <pre><code>for (var i in shapes) {
    google.maps.event.addListener(shapes[i], 'click', function(){alert('hi')});
  }
  </code></pre>
  
  <p>Clicking on the polygons triggers an alert but clicking on the custom overlays does nothing. </p>
  
  <p>How do I make Google Maps API treat the overlays as clickable?</p>