Log the sync communication that happens between client and server.

sync/engine/traffic_logger.h

Index: sync/engine/traffic_logger.h
diff --git a/sync/engine/traffic_logger.h b/sync/engine/traffic_logger.h
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+// Copyright (c) 2012 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.
+
+// This file has the functions to log all the sync related HTTP communication.
+// To get the log run a debug build of chrome with the flag
+// --vmodule=traffic_logger=1.
+
+#ifndef CHROME_BROWSER_SYNC_ENGINE_TRAFFIC_LOGGER_H_
+#define CHROME_BROWSER_SYNC_ENGINE_TRAFFIC_LOGGER_H_
+#pragma once
+
+namespace sync_pb {
+class ClientToServerResponse;
+class ClientToServerMessage;
+}  // namespace sync_pb
+
+namespace browser_sync {
+
+void LogClientToServerMessage(const sync_pb::ClientToServerMessage& msg);
+void LogClientToServerResponse(
+    const sync_pb::ClientToServerResponse& response);
+
+}  // namespace browser_sync
+
+#endif  // CHROME_BROWSER_SYNC_ENGINE_TRAFFIC_LOGGER_H_