[battor agent] Add option to log serial communication

tools/battor_agent/battor_connection_impl.h

 // Copyright 2015 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 TOOLS_BATTOR_AGENT_BATTOR_CONNECTION_IMPL_H_
 #define TOOLS_BATTOR_AGENT_BATTOR_CONNECTION_IMPL_H_
 
+#include <fstream>
 #include <vector>
 
 #include "base/callback_forward.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
 #include "device/serial/serial.mojom.h"
 #include "tools/battor_agent/battor_connection.h"
 #include "tools/battor_agent/battor_error.h"
 #include "tools/battor_agent/battor_protocol_types.h"
@@ skipping 68 matching lines @@
   // The type of message we're looking for in the pending read.
   BattOrMessageType pending_read_message_type_;
 
   // The total number of bytes that we're expecting to send.
   size_t pending_write_length_;
 
   // Threads needed for serial communication.
   scoped_refptr<base::SingleThreadTaskRunner> file_thread_task_runner_;
   scoped_refptr<base::SingleThreadTaskRunner> ui_thread_task_runner_;
 
+  std::fstream serial_log_;
+
   DISALLOW_COPY_AND_ASSIGN(BattOrConnectionImpl);
 };
 
 }  // namespace battor
 
 #endif  // TOOLS_BATTOR_AGENT_BATTOR_CONNECTION_IMPL_H_