Adds settings.cfg for gce-backend.

appengine/gce-backend/proto/config.proto

 // Copyright 2016 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 // GCE Backend config schema.
 
 package gce_backend;
 
 
 // List of InstanceTemplates to manage.
@@ skipping 50 matching lines @@
     // least equal to the minimum size. Leave unspecified
     // for unlimited.
     optional int32 maximum_size = 3;
     // GCE zone to create the instance group manager in.
     // Must be unique per template. e.g. us-central1-b.
     optional string zone = 4;
   }
 
   repeated InstanceGroupManager managers = 1;
 }
+
+
+// GCE Backend Configuration
+message SettingsCfg {
+  // Enable ts_mon based monitoring.
+  optional bool enable_ts_monitoring = 1;
+}