TraySupervisedUser observe user add/switch

TraySupervisedUser should observe user session addition and
switch as well as the user session update. Otherwise, it might
miss some session info as in http://crbug.com/796758, where
user child info is now only set at user session creation with
no user session update followed.

Bug: 796758
Change-Id: Ic275ccfa174a21451077e6ec9225901f188e2a63
Reviewed-on: https://chromium-review.googlesource.com/848020
Commit-Queue: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#527057}

ash/system/supervised/tray_supervised_user.cc

@@ -62,9 +62,16 @@ views::View* TraySupervisedUser::CreateDefaultView(LoginStatus status) {
   return tray_view;
 }
 
+void TraySupervisedUser::OnActiveUserSessionChanged(
+    const AccountId& account_id) {
+  OnUserSessionUpdated(account_id);
+}
+
+void TraySupervisedUser::OnUserSessionAdded(const AccountId& account_id) {
+  OnUserSessionUpdated(account_id);
+}
+
 void TraySupervisedUser::OnUserSessionUpdated(const AccountId& account_id) {
-  // NOTE: This doesn't use OnUserSessionAdded() because the custodian info
-  // isn't available until after the session starts.
   SessionController* session_controller = Shell::Get()->session_controller();
   if (!session_controller->IsUserSupervised())
     return;

ash/system/supervised/tray_supervised_user.h

@@ -28,6 +28,8 @@ class ASH_EXPORT TraySupervisedUser : public SystemTrayItem,
   views::View* CreateDefaultView(LoginStatus status) override;
 
   // SessionObserver:
+  void OnActiveUserSessionChanged(const AccountId& account_id) override;
+  void OnUserSessionAdded(const AccountId& account_id) override;
   void OnUserSessionUpdated(const AccountId& account_id) override;
 
  private: