title: zoom_changed listener doesn't work for me
body: <p>I'm trying to use a zoom listener event in a google maps so that I can resize some axis I have in it. As a beginning, I'm trying to use an alert so that I can see whether if the listener detects a change in the zoom level or not, but I'm not able to get any alert at all. My code is the following:</p>
  
  <pre><code>&lt;html&gt;
  &lt;head&gt;
  &lt;meta name="viewport" content="initial-scale=1.0, user-scalable=no" /&gt;
  &lt;meta http-equiv="content-type" content="text/html; charset=UTF-8"/&gt;
  &lt;title&gt;Google Maps - pygmaps &lt;/title&gt;
  &lt;script type="text/javascript" src="https://maps.googleapis.com/maps/api/js?libraries=visualization&amp;sensor=true_or_false"&gt;&lt;/script&gt;
  &lt;script type="text/javascript"&gt;
      var map;
      function initialize() {
          var centerlatlng = new google.maps.LatLng(49.801674, 11.188139);
          var myOptions = {
              zoom: 18,
              center: centerlatlng,
              scaleControl:true,
              mapTypeId: google.maps.MapTypeId.ROADMAP
          };
  
          map = new google.maps.Map(document.getElementById("map_canvas"), myOptions);
  </code></pre>
  
  <p><strong>* plotting stuff *</strong></p>
  
  <pre><code>google.maps.event.addDomListener(window, 'load',initialize);
  google.maps.event.addDomListener(maps,'zoom_changed', function()
  {
      alert("changed");
  });
  
  &lt;/script&gt;
  &lt;/head&gt;
  &lt;body&gt;
  
      &lt;div style="text-align:center;"&gt;
          &lt;button onclick="draw_axis()"&gt;Enable/Disable Axis&lt;/button&gt; &lt;br&gt;&lt;br&gt;    &lt;div id="log"&gt;&lt;/div&gt;  
      &lt;/div&gt;
      &lt;div id="map_canvas" style="width: 100%; height: 90%;"&gt;&lt;/div&gt;
      &lt;/body&gt;
      &lt;/html&gt;
  </code></pre>
  
  <p>Does anyone see the problem? </p>