 tabindex="1">
        //  </div>
        // TODO(valdrin) support ShadowDOM v1 when upgrading to Polymer v2.0.
        var children;
        if (element.localName === 'content' || element.localName === 'slot') {
          children = Polymer.dom(element).getDistributedNodes();
        } else {
          // Use shadow root if possible, will check for distributed nodes.
          children = Polymer.dom(element.root || element).children;
        }
        for (var i = 0; i < children.length; i++) {
          /