[Sync] Store the past 10 traffic records in memory.

sync/engine/traffic_logger.h

 // 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
 
+#include <string>
+
 namespace sync_pb {
 class ClientToServerResponse;
 class ClientToServerMessage;
 }  // namespace sync_pb
 
 namespace browser_sync {
 
-void LogClientToServerMessage(const sync_pb::ClientToServerMessage& msg);
+namespace sessions {
+class SyncSession;
+}  // namespace sessions
+
+enum TrafficMessageType {
+  CLIENT_TO_SERVER_MESSAGE,
+  CLIENT_TO_SERVER_RESPONSE,
+  UNKNOWN_MESSAGE_TYPE
+};
+
+struct TrafficRecord {
+  // The serialized message.
+  std::string message;
+  TrafficMessageType message_type;
+  // If the message is too big to be kept in memory then it would be trucated.
+  // For now the entire message would be truncated if it is big.
+  // TODO(lipalani): Truncate the specifics to fit with in size.
+  bool truncated;
+
+  TrafficRecord(const std::string& message,
+                TrafficMessageType message_type,
+                bool truncated);
+  TrafficRecord();
+  ~TrafficRecord();
+};
+
+void LogClientToServerMessage(const sync_pb::ClientToServerMessage& msg,
+                              sessions::SyncSession* session);
 void LogClientToServerResponse(
-    const sync_pb::ClientToServerResponse& response);
+    const sync_pb::ClientToServerResponse& response,
+    sessions::SyncSession* session);
 
 }  // namespace browser_sync
 
 #endif  // CHROME_BROWSER_SYNC_ENGINE_TRAFFIC_LOGGER_H_