Both cros-disks and libbrillo have classes to encapsulate child processes. The cros-disks Process class has an extremely narrow API, and we are going to want to get rid of GlibProcess because it depends on glib watches and message loops.

Instead we should implement SandboxedProcess on top of libbrillo's Process, expanding the API on the latter if need be, and then we can remove the cros-disks Process base class and provide easier access to sandboxing for libbrillo users.