Revert of [Service Manager] Get rid of dynamic service discovery

services/service_manager/public/constants.gni

Index: services/service_manager/public/constants.gni
diff --git a/services/service_manager/public/constants.gni b/services/service_manager/public/constants.gni
new file mode 100644
index 0000000000000000000000000000000000000000..19364268367bc59f23872e67d6c2967b286b3b0a
--- /dev/null
+++ b/services/service_manager/public/constants.gni
@@ -0,0 +1,8 @@
+# Copyright 2016 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+declare_args() {
+  # Service package directories are created within this subdirectory.
+  packages_directory = "Packages"
+}