/usr/share/civicrm/CRM/Extension/ is in civicrm-common 4.7.30+dfsg-1ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/civicrm/CRM/Extension/Browser.php
/usr/share/civicrm/CRM/Extension/ClassLoader.php
/usr/share/civicrm/CRM/Extension/Container/
/usr/share/civicrm/CRM/Extension/Container/Basic.php
/usr/share/civicrm/CRM/Extension/Container/Collection.php
/usr/share/civicrm/CRM/Extension/Container/Default.php
/usr/share/civicrm/CRM/Extension/Container/Interface.php
/usr/share/civicrm/CRM/Extension/Container/Static.php
/usr/share/civicrm/CRM/Extension/Downloader.php
/usr/share/civicrm/CRM/Extension/Exception/
/usr/share/civicrm/CRM/Extension/Exception.php
/usr/share/civicrm/CRM/Extension/Exception/DependencyException.php
/usr/share/civicrm/CRM/Extension/Exception/MissingException.php
/usr/share/civicrm/CRM/Extension/Exception/ParseException.php
/usr/share/civicrm/CRM/Extension/Info.php
/usr/share/civicrm/CRM/Extension/Manager/
/usr/share/civicrm/CRM/Extension/Manager.php
/usr/share/civicrm/CRM/Extension/Manager/Base.php
/usr/share/civicrm/CRM/Extension/Manager/Interface.php
/usr/share/civicrm/CRM/Extension/Manager/Module.php
/usr/share/civicrm/CRM/Extension/Manager/Payment.php
/usr/share/civicrm/CRM/Extension/Manager/Report.php
/usr/share/civicrm/CRM/Extension/Manager/Search.php
/usr/share/civicrm/CRM/Extension/Mapper.php
/usr/share/civicrm/CRM/Extension/System.php
/usr/share/civicrm/CRM/Extension/Upgrades.php