title: Polymer core-ajax won't post JSON?
body: <p>I'm using core-ajax to retrieve JSON data just fine. Turning the component around to post back to the server as JSON is another thing altogether. In all cases, and irrespective of the contentType or handleAs parameters passed in, it appears that my JSON object I'm passing in as an input is being converted back to key=value in the server headers.</p>
  
  <p>The code:</p>
  
  <pre><code>var ajax = document.querySelector('core-ajax');
  
  ajax.method = 'POST';
  ajax.handleAs = 'JSON';
  ajax.contentType = 'application/json';
  ajax.params = JSON.stringify(data);
  
  ajax.go();
  </code></pre>
  
  <p>Really straightforward. The logs in Go give me:</p>
  
  <pre><code>2014/07/22 14:23:09 utils.go:139: OPTIONS /1/users/173?access_token=(token)
  2014/07/22 14:23:09 utils.go:124: POST /1/users/173?access_token=(token)
  2014/07/22 14:23:09 users.go:379: full_name=Greg%20Johnson
  </code></pre>
  
  <p>We've verified that there's no transformation happening on our side. Request headers are going out just fine.</p>
  
  <p>I could completely be missing something. How else can we successfully POST out JSON data?</p>