emand when needed.
     * @param {!Event=} optTriggeringEvent (optional) event that triggered the
     * ripple.
     */
    ensureRipple: function(optTriggeringEvent) {
      if (!this.hasRipple()) {
        this._ripple = this._createRipple();
        this._ripple.noink = this.noink;
        var rippleContainer = this._rippleContainer || this.root;
        if (rippleContainer) {
          Polymer.dom(rippleContainer).appendChild(this._ripple);
        }
        if (optTriggeringEvent) {
          // Check