The current version is not able to handle changes to array of markers added via dom-repeat template.

Updated the listener to observe 'iron-items-changed' event at line 534.
The listener is now able to update all the markers when there is a change in items array.
Please note that this code does not update the info window content.
The following code now works correctly.

google-map map="{{map}}" api-key=xxxx latitude="[[lat]]" longitude="[[lon]]">
        <template is="dom-repeat" items="[[array]]">
          <google-map-marker map="[[map]]" latitude="[[item.lat]]" longitude="[[item.lon]]" title="[[item.title]]" ></google-map-marker>
        </template>
      </google-map>

Currently when using dom-repeat template, the info windows are not updated when the item array is updated.
This change to mutation observer allows the info window content to update automatically.