/usr/include/synfig-1.0/synfig/layers/ is in libsynfig-dev 1.2.1-0ubuntu4.
This file is owned by root:root, with mode 0o755.
..
/usr/include/synfig-1.0/synfig/layers/layer_bitmap.h
/usr/include/synfig-1.0/synfig/layers/layer_composite.h
/usr/include/synfig-1.0/synfig/layers/layer_composite_fork.h
/usr/include/synfig-1.0/synfig/layers/layer_duplicate.h
/usr/include/synfig-1.0/synfig/layers/layer_group.h
/usr/include/synfig-1.0/synfig/layers/layer_invisible.h
/usr/include/synfig-1.0/synfig/layers/layer_meshtransform.h
/usr/include/synfig-1.0/synfig/layers/layer_mime.h
/usr/include/synfig-1.0/synfig/layers/layer_motionblur.h
/usr/include/synfig-1.0/synfig/layers/layer_pastecanvas.h
/usr/include/synfig-1.0/synfig/layers/layer_polygon.h
/usr/include/synfig-1.0/synfig/layers/layer_rendering_task.h
/usr/include/synfig-1.0/synfig/layers/layer_shape.h
/usr/include/synfig-1.0/synfig/layers/layer_skeleton.h
/usr/include/synfig-1.0/synfig/layers/layer_skeletondeformation.h
/usr/include/synfig-1.0/synfig/layers/layer_solidcolor.h
/usr/include/synfig-1.0/synfig/layers/layer_sound.h
/usr/include/synfig-1.0/synfig/layers/layer_switch.h