function localStorageSize() {
  return this.requestHandler.create('/session/:sessionId/local_storage/size');
}
protocol bindings to get local_storage size. This command is not part of the official Webdriver
specification and might not be supported for your browser.

@return {Number} The number of items in the storage.

@see  https://github.com/SeleniumHQ/selenium/wiki/JsonWireProtocol#sessionsessionidlocal_storagesize
@type protocol