The system tray menu is supposed to show a warning that your networking connection might be monitored if you are using a VPN or proxy. This doesn't work in mash.

In classic ash the UIProxyConfigService is built by NetworkPrefStateObserver in c/b/chromeos/net, which is called during chrome startup and again after user profile load.

UIProxyConfigService depends on both profile prefs and local state prefs. The mojo prefs service will provide profile prefs soon, but local state prefs are not available. See https://docs.google.com/document/d/1JU8QUWxMEXWMqgkvFUumKSxr7Z-nfq0YvreSJTkMVmU/edit#heading=h.7pmqf27u91lh

(Is there a component or label for pref service?)