title: Non-triggering of onSubmit event in form
body: <p>I have the following polymer dart component</p>
  
  
  
  <pre class="lang-dart prettyprint-override"><code>  &lt;!DOCTYPE html&gt;
  
    &lt;link rel="import" href="../../../shared/ui/delete-button-form.html"&gt;
  
    &lt;polymer-element name='language-combo-form'&gt;
      &lt;template&gt;
        &lt;style&gt;
          /* author style used ie website style*/
        &lt;/style&gt;
  
        &lt;form id='form'
              name='form'
              class='form round-corners'
              on-submit='submit'&gt;
  
          &lt;input id=langTxt type='text'
                 list='langs'
                 value="{{lang}}"
                 placeholder='English'
                 required
                 on-change='{{submit}}'&gt;
  
         &lt;datalist id='langs' &gt;
            &lt;template repeat='{{lang in langs}}'&gt;
              &lt;option value='{{lang}}'&gt;{{lang}}&lt;/option&gt;
            &lt;/template&gt;
         &lt;/datalist&gt;
  
            &lt;button id='submit-btn' type='submit' hidden='hidden'&gt;&lt;/button&gt;
  
        &lt;/form&gt;
  
      &lt;/template&gt;
  
       &lt;script type="application/dart;component=1"&gt;
  
       import 'package:polymer/polymer.dart';
  
  
        import 'package:epimss_polymer/events.dart';
  
        import 'dart:html';
  
        @CustomTag( 'language-combo-form')
        class LanguageComboForm extends PolymerElement
        {
          @observable String lang = '';
  
          List&lt;String&gt; langs = [  '', 
                                      'Basque', 'Bulgarian',
                                      'Catalan', 'Chinese - Simplified'
  
                                  ];
  
          LanguageComboForm.created() : super.created();
  
          bool get applyAuthorStyles =&gt; true;
  
          void submit ( Event e, var detail, Node target )
          {
            //$['submit-btn'].click();
  
            $['form']
              .onSubmit
              .listen( ( Event e )
                   {
                      e.preventDefault();
  
                      dispatchEvent(
                                new CustomEvent( LANGUAGE_COMBO_FORM_EVENT,
                                                 detail:{'lang':lang}));
  
                      print( 'submitted from onSubmit: $lang' );
  
                   });        
          }
  
  
        }
  
      &lt;/script&gt;
    &lt;/polymer-element&gt;
  </code></pre>
  
  <p>However, the code inside the submit method ...</p>
  
  <pre class="lang-dart prettyprint-override"><code>  $['form']
              .onSubmit
              .listen( ( Event e )
                   {
                      e.preventDefault();
  
                      dispatchEvent(
                                new CustomEvent( LANGUAGE_COMBO_FORM_EVENT,
                                                 detail:{'lang':lang}));
  
                      print( 'submitted from onSubmit: $lang' );
  
                   });
  </code></pre>
  
  <p>is Not being triggered.</p>
  
  <p>If I uncomment the first line in the submit method the for is submitted as indicated by a refresh of the page but still the nothing is printed to the console.</p>