20cc535ba6
Fixes a bug introduced in CL/432455486, which stopped saving explicit inertias if they were inferred from geoms. But if we don't save inertias then we need to save mass/density specifiers. BEGIN_PUBLIC xml_native_writer saves geom mass or density, if specified. END_PUBLIC PiperOrigin-RevId: 450667775 Change-Id: Ibb5b269b58f1143013091729642bb501243ed943