message: Ensures that all simulated TCP packets are at least 4 bytes.
  Cr-Commit-Position: refs/heads/master@{#30780}
diff: @@ -146,9 +146,11 @@ void TcpMessageRouteImpl::SendMessage(size_t size,
  }
  size_t data_left = size;
  size_t kMaxPacketSize = 1200;
  + size_t kMinPacketSize = 4;
  Message message{std::move(handler)};
  while (data_left > 0) {
  - size_t packet_size = std::min(data_left, kMaxPacketSize);
  + size_t packet_size =
  + std::max(kMinPacketSize, std::min(data_left, kMaxPacketSize));
  int fragment_id = next_fragment_id_++;
  pending_.push_back(MessageFragment{fragment_id, packet_size});
  message.pending_fragment_ids.insert(fragment_id);
  