buttonClick_(action, origin, contentBlob, event) {
    var elem = goog.dom.getElement(constants.ElementId.BODY);
    var target = event.target;

    if (target instanceof HTMLImageElement) {
      target = target.parentElement;
    }

    if (target instanceof Element) {
      if (goog.dom.classlist.contains(target, constants.CssClass.CANCEL)) {
        this.close();
      }
    }
  }
@param {constants.Actions} action
@param {string} origin
@param {messages.BridgeMessageRequest} contentBlob
@param {Event} event
@private