Revert of Merge duplicate code in invalidation helper.

sync/tools/invalidation_helper.h

Index: sync/tools/invalidation_helper.h
diff --git a/sync/tools/invalidation_helper.h b/sync/tools/invalidation_helper.h
new file mode 100644
index 0000000000000000000000000000000000000000..c26c6ef26ab7f19faa511000c0a8e39308475224
--- /dev/null
+++ b/sync/tools/invalidation_helper.h
@@ -0,0 +1,21 @@
+// Copyright 2014 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.
+
+#ifndef SYNC_TOOLS_INVALIDATION_HELPER_H_
+#define SYNC_TOOLS_INVALIDATION_HELPER_H_
+
+#include "components/invalidation/public/invalidation_util.h"
+#include "google/cacheinvalidation/include/types.h"
+#include "sync/internal_api/public/base/model_type.h"
+
+namespace syncer {
+
+bool RealModelTypeToObjectId(ModelType model_type,
+                             invalidation::ObjectId* object_id);
+
+ObjectIdSet ModelTypeSetToObjectIdSet(ModelTypeSet model_types);
+
+}
+
+#endif  // SYNC_TOOLS_INVALIDATION_HELPER_H