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

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
index 5cb8ffa81b4a3abec1d301d1522ab4bbd921e315..34f76b4ac33c8b1189ca61a8010148f6e9f39f8b 100644
--- a/sync/engine/traffic_logger.h
+++ b/sync/engine/traffic_logger.h
@@ -10,6 +10,8 @@
 #define CHROME_BROWSER_SYNC_ENGINE_TRAFFIC_LOGGER_H_
 #pragma once
 
+#include <string>
+
 namespace sync_pb {
 class ClientToServerResponse;
 class ClientToServerMessage;
@@ -17,9 +19,37 @@ class ClientToServerMessage;
 
 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