/usr/share/doc/linux-tools-3.19.0-51-lowlatency/changelog.Debian.gz is in linux-tools-3.19.0-51-lowlatency 3.19.0-51.58~14.04.1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/linux-tools-3.19.0-51-lowlatency/../linux-lts-vivid-tools-3.19.0-51/changelog.Debian.gz