/usr/include/mission-control-5.5/mission-control-plugins/ is in libmission-control-plugins-dev 1:5.16.3-1ubuntu6.
This file is owned by root:root, with mode 0o755.
..
/usr/include/mission-control-5.5/mission-control-plugins/account-storage.h
/usr/include/mission-control-5.5/mission-control-plugins/account.h
/usr/include/mission-control-5.5/mission-control-plugins/dbus-acl.h
/usr/include/mission-control-5.5/mission-control-plugins/debug.h
/usr/include/mission-control-5.5/mission-control-plugins/dispatch-operation-policy.h
/usr/include/mission-control-5.5/mission-control-plugins/dispatch-operation.h
/usr/include/mission-control-5.5/mission-control-plugins/loader.h
/usr/include/mission-control-5.5/mission-control-plugins/mcp-signals-marshal.h
/usr/include/mission-control-5.5/mission-control-plugins/mission-control-plugins.h
/usr/include/mission-control-5.5/mission-control-plugins/request-policy.h
/usr/include/mission-control-5.5/mission-control-plugins/request.h