function showSnackbar(message, timeoutMillis = 4000) {
  snackbar.labelText = message;
  snackbar.timeoutMs = timeoutMillis;
  snackbar.open();
}
Display a snackbar message on the screen.

@param {string} message The message to be displayed.
@param {number} timeoutMillis How many millliseconds the message
  will stay on the screen before disappearing.