Implement a server-side config service interface.

luci_config/server/cfgclient/backend/meta.go

+// 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.
+
+package backend
+
+// Meta is backend metadata about a single configuration file.
+type Meta struct {
+        // ConfigSet is the item's config set.
+        ConfigSet string
+        // Path is the item's path within its config set.
+        Path string
+
+        // ContentHash is the content hash.
+        ContentHash string
+        // Revision is the revision string.
+        Revision string
+}