/usr/include/Swiften/Base/ is in libswiften-dev 2.0+dev6-1+b1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/Swiften/Base/API.h
/usr/include/Swiften/Base/Algorithm.h
/usr/include/Swiften/Base/BoostFilesystemVersion.h
/usr/include/Swiften/Base/BoostRandomGenerator.h
/usr/include/Swiften/Base/ByteArray.h
/usr/include/Swiften/Base/Concat.h
/usr/include/Swiften/Base/DateTime.h
/usr/include/Swiften/Base/Error.h
/usr/include/Swiften/Base/IDGenerator.h
/usr/include/Swiften/Base/Log.h
/usr/include/Swiften/Base/Paths.h
/usr/include/Swiften/Base/Platform.h
/usr/include/Swiften/Base/RandomGenerator.h
/usr/include/Swiften/Base/SafeAllocator.h
/usr/include/Swiften/Base/SafeByteArray.h
/usr/include/Swiften/Base/SafeString.h
/usr/include/Swiften/Base/SimpleIDGenerator.h
/usr/include/Swiften/Base/StartStopper.h
/usr/include/Swiften/Base/String.h
/usr/include/Swiften/Base/URL.h
/usr/include/Swiften/Base/WindowsRegistry.h
/usr/include/Swiften/Base/boost_bsignals.h
/usr/include/Swiften/Base/foreach.h
/usr/include/Swiften/Base/format.h
/usr/include/Swiften/Base/sleep.h