Implement a server-side config service interface.

luci_config/server/cfgclient/backend/meta.go

Index: luci_config/server/cfgclient/backend/meta.go
diff --git a/luci_config/server/cfgclient/backend/meta.go b/luci_config/server/cfgclient/backend/meta.go
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index 0000000000000000000000000000000000000000..9ef9be9b036a27d97f8240b9fa11d19da9ec5c35
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+++ b/luci_config/server/cfgclient/backend/meta.go
@@ -0,0 +1,18 @@
+// 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
+}