code: @SuppressWarnings("WeakerAccess")
    public SnackbarBuilder manualDismissCallback(final SnackbarManualDismissCallback callback) {
      callbacks.add(new SnackbarCallback() {
        public void onSnackbarManuallyDismissed(Snackbar snackbar) {
          callback.onSnackbarManuallyDismissed(snackbar);
        }
      });
      return this;
    }
docs: Set the callback to be informed of the Snackbar being dismissed manually, due to a call to dismiss().
  
  @param callback The callback.
  @return This instance.