message: Add error information to BenchmarkEvents
diff: @@ -496,8 +496,10 @@ message BenchmarkError {
  optional int32 exit_code = 2;
  // Signal the process received.
  optional int32 signal = 3;
  - // Handled error.
  + // Handled tflite error.
  repeated ErrorCode error_code = 4;
  + // Mini-benchmark error code.
  + optional int32 mini_benchmark_error_code = 5;
  }
  // Top-level benchmarking event stored on-device. All events for a model are
  