port to use centralized constants files, and add input validation

constants.h

Index: constants.h
diff --git a/constants.h b/constants.h
deleted file mode 100644
index cc0e89ecf71d367333c7881bd716733b67b69a5b..0000000000000000000000000000000000000000
--- a/constants.h
+++ /dev/null
@@ -1,13 +0,0 @@
-// Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-#ifndef LOGIN_MANAGER_CONSTANTS_H_
-#define LOGIN_MANAGER_CONSTANTS_H_
-
-namespace login_manager {
-extern const char *kSessionManagerInterface;
-extern const char *kSessionManagerServicePath;
-extern const char *kSessionManagerServiceName;
-}  // namespace login_manager
-
-#endif  // LOGIN_MANAGER_CONSTANTS_H_