message: Fix for potential infinite loop in TCP traffic simulator.
  For stream sizes that were not multiple of 4, we could end up causing
  a size_t wraparound which resulted in an infinite loop.
  Cr-Commit-Position: refs/heads/master@{#31503}
diff: @@ -144,15 +144,16 @@ void TcpMessageRouteImpl::SendMessage(size_t size,
  cwnd_ = 10;
  ssthresh_ = INFINITY;
  }
  - size_t data_left = size;
  - size_t kMaxPacketSize = 1200;
  - size_t kMinPacketSize = 4;
  + int64_t data_left = static_cast<int64_t>(size);
  + int64_t kMaxPacketSize = 1200;
  + int64_t kMinPacketSize = 4;
  Message message{std::move(handler)};
  while (data_left > 0) {
  - size_t packet_size =
  - std::max(kMinPacketSize, std::min(data_left, kMaxPacketSize));
  + int64_t packet_size = std::min(data_left, kMaxPacketSize);
  int fragment_id = next_fragment_id_++;
  - pending_.push_back(MessageFragment{fragment_id, packet_size});
  + pending_.push_back(MessageFragment{
  + fragment_id,
  + static_cast<size_t>(std::max(kMinPacketSize, packet_size))});
  message.pending_fragment_ids.insert(fragment_id);
  data_left -= packet_size;
  }
  