function isSilk() {
  // As of Silk 93, Silk does not identify itself in userAgentData.brands.
  // When Silk changes this behavior, update this method to call
  // matchUserAgentDataBrand (akin to isChrome, etc.)
  return util.matchUserAgent('Silk');
}
For more information, see:
http://docs.aws.amazon.com/silk/latest/developerguide/user-agent.html
@return {boolean} Whether the user's browser is Silk.