Experimente este comando
dpkg -S $(which unity-webapps-runner)
A saída do comando acima mostra
unity-webapps-service: /usr/bin/unity-webapps-runner
Portanto, unity-webapps-runner
pertence a unity-webapps-service
package.
Obtenha a fonte do pacote unity-webapps-service
executando o comando abaixo,
apt-get source unity-webapps-service