static modifyNodeAttribute(node, action, attribute, value) {
    if (action === 'remove') {
      delete node.attributes[attribute];
    } else if (action === 'add' || action === 'replace') {
      node.attributes[attribute] = value;
    }
  }
@param {!shaka.extern.xml.Node} node
@param {string} action
@param {string} attribute
@param {string} value