message: Use a default member initializer for external_command_encoder_
diff: @@ -184,7 +184,6 @@ class Delegate {
  options_.wait_type = TFLGpuDelegateWaitType::TFLGpuDelegateWaitTypePassive;
  }
  metal_device_ = MTLCreateSystemDefaultDevice();
  - external_command_encoder_ = nil;
  command_queue_ = [metal_device_ newCommandQueue];
  if (options_.wait_type == TFLGpuDelegateWaitType::TFLGpuDelegateWaitTypeAggressive) {
  gpu_alarm_clock_ = std::unique_ptr<GpuAlarmClock>(new GpuAlarmClock(command_queue_));
  @@ -633,7 +632,7 @@ class Delegate {
  std::vector<BufferDescriptor> graph_inputs_;
  std::vector<BufferDescriptor> graph_outputs_;
  - id<MTLComputeCommandEncoder> external_command_encoder_;
  + id<MTLComputeCommandEncoder> external_command_encoder_ = nil;
  std::function<id<MTLComputeCommandEncoder>(bool is_last)> control_encoder_;
  id<MTLCommandQueue> command_queue_;
  std::unique_ptr<GpuAlarmClock> gpu_alarm_clock_;
  