/usr/share/doc/libgl1-mesa-glx-lts-xenial/changelog.Debian.gz is in libgl1-mesa-glx-lts-xenial 11.2.0-1ubuntu2~trusty2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libgl1-mesa-glx-lts-xenial/../libglapi-mesa-lts-xenial/changelog.Debian.gz