cros: Remove supervised user methods from SystemTrayDelegate

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 0dd24b166e741fd3f257e86c97ddc8f82d416865..fbebb372a82b114c0760a278728d10b400e10def 100644
--- a/ash/public/interfaces/session_controller.mojom
+++ b/ash/public/interfaces/session_controller.mojom
@@ -71,7 +71,8 @@ enum CycleUserDirection {
   PREVIOUS,  // Cycle to the previous user.
 };
 
-// Info about a user session in ash.
+// Info about a user session in ash. May be sent repeatedly for a single user
+// because individual fields may change (e.g. the avatar image or custodians).
 struct UserSession {
   // A user session id for the user session. It is generated by session manager
   // (chrome) when a user session starts and never changes during the lifetime
@@ -85,6 +86,14 @@ struct UserSession {
   string display_email;
   gfx.mojom.ImageSkia avatar;
 
+  // For supervised users only, the email address of the custodian account.
+  // Empty for non-supervised users. Available after profile is loaded.
+  string custodian_email;
+
+  // For supervised users only, the email address of the second custodian
+  // account, if any. Available after profile is loaded.
+  string second_custodian_email;
+
   // Whether the settings icon should be enabled in the system tray menu.
   // Usually true after login, but can be false for specialized user sessions
   // (e.g. adding supervised users).