UserSessionManager: Ensure EasyUnlockService is non-null.

Bug: 895937
Change-Id: I7eec1edce0fe9dd2c8e444b51dcd81fe34bcc1ed
Reviewed-on: https://chromium-review.googlesource.com/c/1287433Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Reviewed-by: Jacob Dufault <jdufault@chromium.org>
Commit-Queue: Jacob Dufault <jdufault@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600792}

chrome/browser/chromeos/login/session/user_session_manager.cc

@@ -1943,7 +1943,8 @@ void UserSessionManager::OnEasyUnlockKeyOpsFinished(const std::string& user_id,
   const user_manager::User* user = user_manager::UserManager::Get()->FindUser(
       AccountId::FromUserEmail(user_id));
   EasyUnlockService* easy_unlock_service = EasyUnlockService::GetForUser(*user);
-  easy_unlock_service->CheckCryptohomeKeysAndMaybeHardlock();
+  if (easy_unlock_service)
+    easy_unlock_service->CheckCryptohomeKeysAndMaybeHardlock();
 
   NotifyEasyUnlockKeyOpsFinished();
 }