title: Polymer 1.0: Wait for multiple iron-ajax requests to finish
body: <p>I have multiple iron-ajax tags on the page e.g.:</p>
  
  <pre><code>&lt;iron-ajax
              auto
              id="ajaxCall1"
              url="/data/test1.json"
              handle-as="json"
              on-response="_myAjaxCall1ResponseHandler"
              last-response="{{_myAjaxCall1LastResponse}}"
              debounce-duration="300"&gt;
  &lt;/iron-ajax&gt;
  
  &lt;iron-ajax
              auto
              id="ajaxCall2"
              url="/data/test2.json"
              handle-as="json"
              on-response="_myAjaxCall2ResponseHandler"
              last-response="{{_myAjaxCall2LastResponse}}"
              debounce-duration="300"&gt;
   &lt;/iron-ajax&gt;
  </code></pre>
  
  <p>How can I wait for both requests to be completed before I do another action? I don't care about the order of requests, just they they are both completed. </p>
  
  <p>Thanks.</p>