code: private void obtainOverrideNavigationIcon() {
          boolean overrideNavigationIcon =
                  ThemeUtil.getBoolean(this, R.attr.overrideNavigationIcon, true);
          overrideNavigationIcon(overrideNavigationIcon);
      }
docs: Obtains, whether the behavior of the navigation icon should be overridden, or not, from the
  activity's theme.