conditionally load webcomponent polyfills

index.html

<script>
    if ('registerElement' in document
      && 'createShadowRoot' in HTMLElement.prototype
      && 'import' in document.createElement('link')
      && 'content' in document.createElement('template')) {
      // We're using a browser with native WC support!
    } else {
      document.write('<script src="//cdnjs.cloudflare.com/ajax/libs/webcomponentsjs/0.5.1-1/webcomponents.min.js"><\/script>');
    }
</script>