Remove unused methods and member variables from QuicConnection. I checked and Chromium isn't using any of these. This change removes: * An overload of `AdjustNetworkParameters`. * The const overload of `context()`. * `per_packet_options()`. * The `PendingPathChallenge` struct. * `GetLeastUnacked()`. * `SendGenericPathProbePacket()`. * `largest_seen_packet_with_stop_waiting_`. * `received_path_challenge_payloads_`. * `last_control_frame_id_`. A comment is also added to `SendPing`. PiperOrigin-RevId: 813394476

diff --git a/quiche/quic/core/quic_connection.cc b/quiche/quic/core/quic_connection.cc
index c70d676..8a2aa77 100644
--- a/quiche/quic/core/quic_connection.cc
+++ b/quiche/quic/core/quic_connection.cc

@@ -2431,10 +2431,6 @@
       clock_->ApproximateNow());
 }
 
-QuicPacketNumber QuicConnection::GetLeastUnacked() const {
-  return sent_packet_manager_.GetLeastUnacked();
-}
-
 bool QuicConnection::HandleWriteBlocked() {
   if (!writer_->IsWriteBlocked()) {
     return false;

diff --git a/quiche/quic/core/quic_connection.h b/quiche/quic/core/quic_connection.h
index afcf107..a0e2d1c 100644
--- a/quiche/quic/core/quic_connection.h
+++ b/quiche/quic/core/quic_connection.h

@@ -625,8 +625,6 @@
   // information.
   void AdjustNetworkParameters(
       const SendAlgorithmInterface::NetworkParams& params);
-  void AdjustNetworkParameters(QuicBandwidth bandwidth, QuicTime::Delta rtt,
-                               bool allow_cwnd_to_decrease);
 
   // Install a loss detection tuner. Must be called before OnConfigNegotiated.
   void SetLossDetectionTuner(
@@ -1376,6 +1374,8 @@
 
   void SetSourceAddressTokenToSend(absl::string_view token);
 
+  // Used by Chromium clients to send PING frames when there are no outstanding
+  // requests. TODO(ianswett): Consider removing this functionality.
   void SendPing() {
     SendPingAtLevel(framer().GetEncryptionLevelToSendApplicationData());
   }
@@ -1395,7 +1395,6 @@
   void QuicBugIfHasPendingFrames(QuicStreamId id) const;
 
   QuicConnectionContext* context() override { return &context_; }
-  const QuicConnectionContext* context() const { return &context_; }
 
   void set_context_listener(
       std::unique_ptr<QuicConnectionContextListener> listener) {
@@ -1561,9 +1560,6 @@
   //      change.
   virtual QuicSocketAddress GetEffectivePeerAddressFromCurrentPacket() const;
 
-  // Returns the current per-packet options for the connection.
-  PerPacketOptions* per_packet_options() { return per_packet_options_; }
-
   AddressChangeType active_effective_peer_migration_type() const {
     return active_effective_peer_migration_type_;
   }
@@ -1630,11 +1626,6 @@
     kMaxValue,
   };
 
-  struct QUICHE_EXPORT PendingPathChallenge {
-    QuicPathFrameBuffer received_path_challenge;
-    QuicSocketAddress peer_address;
-  };
-
   struct QUICHE_EXPORT PathState {
     PathState() = default;
 
@@ -1933,10 +1924,6 @@
   // acks and pending writes if an ack opened the congestion window.
   void MaybeSendInResponseToPacket();
 
-  // Gets the least unacked packet number, which is the next packet number to be
-  // sent if there are no outstanding packets.
-  QuicPacketNumber GetLeastUnacked() const;
-
   // Sets the ping alarm to the appropriate value, if any.
   void SetPingAlarm();
 
@@ -1989,11 +1976,6 @@
   // Updates the release time into the future.
   void UpdateReleaseTimeIntoFuture();
 
-  // Sends generic path probe packet to the peer. If we are not IETF QUIC, will
-  // always send a padded ping, regardless of whether this is a request or not.
-  bool SendGenericPathProbePacket(QuicPacketWriter* probing_writer,
-                                  const QuicSocketAddress& peer_address);
-
   // Called when an ACK is about to send. Resets ACK related internal states,
   // e.g., cancels ack_alarm_, resets
   // num_retransmittable_packets_received_since_last_ack_sent_ etc.
@@ -2263,9 +2245,6 @@
   // number spaces.
   QuicPacketNumber largest_seen_packets_with_ack_[NUM_PACKET_NUMBER_SPACES];
 
-  // Largest packet number sent by the peer which had a stop waiting frame.
-  QuicPacketNumber largest_seen_packet_with_stop_waiting_;
-
   // Collection of packets which were received before encryption was
   // established, but which could not be decrypted.  We buffer these on
   // the assumption that they could not be processed because they were
@@ -2350,15 +2329,6 @@
   // Time this connection can release packets into the future.
   QuicTime::Delta release_time_into_future_;
 
-  // Payloads that were received in the most recent probe. This needs to be a
-  // Deque because the peer might no be using this implementation, and others
-  // might send a packet with more than one PATH_CHALLENGE, so all need to be
-  // saved and responded to.
-  // TODO(danzh) deprecate this field when deprecating
-  // --quic_send_path_response.
-  quiche::QuicheCircularDeque<QuicPathFrameBuffer>
-      received_path_challenge_payloads_;
-
   // When we receive a RETRY packet or some INITIAL packets, we replace
   // |server_connection_id_| with the value from that packet and save off the
   // original value of |server_connection_id_| into
@@ -2449,9 +2419,6 @@
   // from the peer.
   uint32_t last_flow_label_received_ = 0;
 
-  // Id of latest sent control frame. 0 if no control frame has been sent.
-  QuicControlFrameId last_control_frame_id_ = kInvalidControlFrameId;
-
   RetransmittableOnWireBehavior retransmittable_on_wire_behavior_ = DEFAULT;
 
   // TODO(danzh) remove `current_packet_content_` and