cros: Use SessionController for lock starting code

chrome/browser/chromeos/login/lock/screen_locker.h

Index: chrome/browser/chromeos/login/lock/screen_locker.h
diff --git a/chrome/browser/chromeos/login/lock/screen_locker.h b/chrome/browser/chromeos/login/lock/screen_locker.h
index 07f65bb99bebfc0f465796f9d8d9d493c1595022..b9b8125234f8b9e1bfeb6d9adda16d3b1c3e8a5f 100644
--- a/chrome/browser/chromeos/login/lock/screen_locker.h
+++ b/chrome/browser/chromeos/login/lock/screen_locker.h
@@ -145,6 +145,10 @@ class ScreenLocker : public AuthStatusConsumer {
   // Looks up user in unlock user list.
   const user_manager::User* FindUnlockUser(const AccountId& account_id);
 
+  // Used as a callback to be invoked after ash finishes post lock animation
+  // and fully locked.
+  void OnLockAnimationFinished();
+
   // WebUIScreenLocker instance in use.
   std::unique_ptr<WebUIScreenLocker> web_ui_;