Under classic/single-process mash:

• The dbus::Bus instance is created in chrome and passed to ash in ShellInitParams.
• Access to D-Bus clients is restricted to clients that will eventually be owned by the ash process.

Under multi-process ash (mash):

• AshDBusHelper creates its own dbus thread and dbus::Bus instance.
• The D-Bus clients created in AshService are owned by the ash process.
• The D-Bus services in AshDBusServices are owned by the ash process.

See //ash/README.md for details on mash. See Chrome OS D-Bus Usage in Chrome for information about adding D-Bus services.