/usr/share/php/Composer/Installer/ is in composer 1.0.0~beta2-1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/php/Composer/Installer/BinaryInstaller.php
/usr/share/php/Composer/Installer/InstallationManager.php
/usr/share/php/Composer/Installer/InstallerEvent.php
/usr/share/php/Composer/Installer/InstallerEvents.php
/usr/share/php/Composer/Installer/InstallerInterface.php
/usr/share/php/Composer/Installer/LibraryInstaller.php
/usr/share/php/Composer/Installer/MetapackageInstaller.php
/usr/share/php/Composer/Installer/NoopInstaller.php
/usr/share/php/Composer/Installer/PackageEvent.php
/usr/share/php/Composer/Installer/PackageEvents.php
/usr/share/php/Composer/Installer/PearBinaryInstaller.php
/usr/share/php/Composer/Installer/PearInstaller.php
/usr/share/php/Composer/Installer/PluginInstaller.php
/usr/share/php/Composer/Installer/ProjectInstaller.php
/usr/share/php/Composer/Installer/SuggestedPackagesReporter.php