In QuicSentPacketManager::OnPacketSent and QuicUnackedPacketMap::AddSentPacket, make it clear that which part of the serialized packet can be modified. I plan to move the debug_visitor_->OnPacketSent in QuicConnection to be after QuicSentPacketManager::OnPacketSent, such that the recorded traces reflects the state after the packet is sent. This is a prerequisite for that. PiperOrigin-RevId: 331256790 Change-Id: I731983563a27ca068fd797e775e4039e4dd26309