computeMemberBounds method
(undocumented) Compute the union of the Bounds of this Placeholder's parent's Group.memberParts. If there are no members, this returns a Rect with Width and Height of zero and an X and Y that are this panel's original location in document coordinates. This is only called when the Placeholder is inside a Group.
Implementation
_i3.Rect computeMemberBounds(_i3.Rect result) => _i4.callMethod(
      this,
      'computeMemberBounds',
      [result],
    );