Currently the chrome browser process talks to cras over D-Bus.

Input/output device switching, gain/volume setting. CrasAudioHandler caches volumes, device lists, etc.

CrasAudioHandler supports chrome.audio extension service (used by hotrod GVC app).

All access in //ash is via SystemTrayDelegate / VolumeControlDelegate.

Startup involves reading prefs, policy settings, and querying for audio notes, among other things.

Plan: Change dbus client library to support both chrome and ash talking to cras