Chromad: Add authentication flow

ash/public/interfaces/session_controller.mojom

Index: ash/public/interfaces/session_controller.mojom
diff --git a/ash/public/interfaces/session_controller.mojom b/ash/public/interfaces/session_controller.mojom
index 3d8f6032d2ed5c351282f8fd5ffc2e67bbfbacf7..3c919dae7827838e12aa7e17b446634234d2cee3 100644
--- a/ash/public/interfaces/session_controller.mojom
+++ b/ash/public/interfaces/session_controller.mojom
@@ -59,6 +59,9 @@ enum UserType {
 
   // Android app in kiosk mode, logs in without authentication.
   ARC_KIOSK,
+
+  // Active Directory user. Authenticates against Active Directory server.
+  AD,

[dcheng, 2016/12/20 09:26:26]

Nit: Let's write this as ACTIVE_DIRECTORY, per the style guide convention of
avoiding abbreviations. Similar comment throughout the rest of this CL (AdUser
=> ActiveDirectoryUser, IsADUser => IsActiveDirectoryUser, etc)

[Roman Sorokin (ftl), 2016/12/20 12:43:59]

Done.

 };
 
 // Info about a user session in ash.