stringifyType = function(type) {
    if (typeof type === 'string') {
      return type;
    } else {
      return ee.Types.classToName(type);
    }
  }
Creates a CustomFunction calling a given native function with the specified
return type and argument types and auto-generated argument names.

@param {Function} func The native function to wrap.
@param {string|Function} returnType The type of the return value, either
    as a string or a constructor/class reference.
@param {Array.<string|Function>} arg_types The types of the arguments,
    either as strings or constructor/class references.
@return {!ee.CustomFunction} The constructed CustomFunction.