message: rollback it, and remove auto
diff: @@ -43,7 +43,7 @@ class GrpcWorkerCache : public WorkerCachePartial {
  void* tag;
  bool ok;
  while (completion_queue_.Next(&tag, &ok)) {
  - auto callback_tag = static_cast<GrpcClientCQTag*>(tag);
  + GrpcClientCQTag* callback_tag = static_cast<GrpcClientCQTag*>(tag);
  callback_tag->OnCompleted(ok);
  }
  });
  @@ -67,7 +67,7 @@ class GrpcWorkerCache : public WorkerCachePartial {
  if (target == local_target_) {
  return local_worker_;
  } else {
  - auto channel = channel_cache_->FindWorkerChannel(target);
  + SharedGrpcChannelPtr channel = channel_cache_->FindWorkerChannel(target);
  if (!channel) return nullptr;
  return NewGrpcRemoteWorker(&live_rpc_counter_, channel,
  &completion_queue_, &logger_);
  