title: paper-button with type="submit" within form doesn't submit?
body: <p>I am trying to use <code>paper-button</code> with <code>type</code> attribute set to <code>submit</code> (as one would do with <code>button</code> element) to submit the enclosing <code>form</code>, but for some reason it is unable to submit the form. Is this a bug or feature? </p>
  
  <p>How to make <code>paper-button</code> submit the form?</p>
  
  <p>PS: I am in dart land (not js).</p>