This question was answered on the google forum "chromedriver-users". This is the working answer:
Map<String, Object> prefs = new HashMap<String, Object>();
prefs.put("profile.default_content_setting_values.notifications", 2);
ChromeOptions options = new ChromeOptions();
options.setExperimentalOption("prefs", prefs);
WebDriver driver = new ChromeDriver(options);
source
share