Update the AvatarMenu when a supervised user's custodian info changes.

chrome/browser/supervised_user/supervised_user_service_observer.h

Index: chrome/browser/supervised_user/supervised_user_service_observer.h
diff --git a/chrome/browser/supervised_user/supervised_user_service_observer.h b/chrome/browser/supervised_user/supervised_user_service_observer.h
index 27580f6b8e4075b784c126c879c03593ada92824..7d9d61c210960221c824780af1c986295d077f06 100644
--- a/chrome/browser/supervised_user/supervised_user_service_observer.h
+++ b/chrome/browser/supervised_user/supervised_user_service_observer.h
@@ -11,6 +11,10 @@ class SupervisedUserServiceObserver {
   // content pack is added, or the default fallback behavior is changed.
   virtual void OnURLFilterChanged() {}
 
+  // Called when information about the supervised user's custodian is changed,
+  // e.g. the display name.
+  virtual void OnCustodianInfoChanged() {}
+
  protected:
   virtual ~SupervisedUserServiceObserver() {}
 };