dexopt_chroot_setup is a component of ART Service. It sets up the chroot environment for Pre-reboot Dexopt, to dexopt apps on a best-effort basis before the reboot after a Mainline update or an OTA update is downloaded, to support seamless updates.
It requires elevated permissions that are not available to system_server, such as mounting filesystems. It publishes a binder interface that is internal to ART Service's Java code.