/usr/share/doc/libgtksourceview3.0-doc/html is in libgtksourceview-3.0-doc 3.4.1-0ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libgtksourceview3.0-doc/../../gtk-doc/html/gtksourceview-3.0