function mapChildren(children, func, context) {
    if (children == null) {
      return children;
    }

    var result = [];
    var count = 0;
    mapIntoArray(children, result, '', '', function (child) {
      return func.call(context, child, count++);
    });
    return result;
  }
Maps children that are typically specified as `props.children`.

See https://reactjs.org/docs/react-api.html#reactchildrenmap

The provided mapFunction(child, index) will be called for each
leaf child.

@param {?*} children Children tree container.
@param {function(*, int)} func The map function.
@param {*} context Context for mapFunction.
@return {object} Object containing the ordered map of results.