Make the BattOr agent retry start tracing when we fail to read an ack

tools/battor_agent/battor_error.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_ERROR_H_
 #define TOOLS_BATTOR_AGENT_BATTOR_ERROR_H_
 
 #include <string>
 
 namespace battor {
 
 // A BattOrError is an error that occurs when communicating with a BattOr.
 enum BattOrError {
   BATTOR_ERROR_NONE,
   BATTOR_ERROR_CONNECTION_FAILED,
   BATTOR_ERROR_TIMEOUT,
   BATTOR_ERROR_SEND_ERROR,
   BATTOR_ERROR_RECEIVE_ERROR,
   BATTOR_ERROR_UNEXPECTED_MESSAGE,
   BATTOR_ERROR_TOO_MANY_INIT_RETRIES,
+  BATTOR_ERROR_TOO_MANY_START_TRACING_RETRIES,
 };
 
 std::string BattOrErrorToString(BattOrError error);
 
 }
 
 #endif  // TOOLS_BATTOR_AGENT_BATTOR_ERROR_H_