IconTheme.merge({Key key, @required BuildContext context, @required IconThemeData data, @required Widget child })

Creates an icon theme that controls the color, opacity, and size of descendant widgets, and merges in the current icon theme, if any.

The context, data, and child arguments must not be null.

Source 

factory IconTheme.merge({
  Key key,
  @required BuildContext context,
  @required IconThemeData data,
  @required Widget child
}) {
  return new IconTheme(
    key: key,
    data: IconTheme.of(context).merge(data),
    child: child
  );
}