Add a debug callback at the end of QuicSentPacketManager::FromConfig.

This is primarily for logging in netlogs (see https://bugs.chromium.org/p/chromium/issues/detail?id=1291452).

PiperOrigin-RevId: 424941652

quic/core/quic_sent_packet_manager.cc

diff --git a/quic/core/quic_sent_packet_manager.cc b/quic/core/quic_sent_packet_manager.cc
index e8f1aa8..55dbe05 100644
--- a/quic/core/quic_sent_packet_manager.cc
+++ b/quic/core/quic_sent_packet_manager.cc
@@ -335,6 +335,15 @@
   if (network_change_visitor_ != nullptr) {
     network_change_visitor_->OnCongestionChange();
   }
+
+  if (debug_delegate_ != nullptr) {
+    DebugDelegate::SendParameters parameters;
+    parameters.congestion_control_type =
+        send_algorithm_->GetCongestionControlType();
+    parameters.use_pacing = using_pacing_;
+    parameters.initial_congestion_window = initial_congestion_window_;
+    debug_delegate_->OnConfigProcessed(parameters);
+  }
 }
 
 void QuicSentPacketManager::ApplyConnectionOptions(

quic/core/quic_sent_packet_manager.h

diff --git a/quic/core/quic_sent_packet_manager.h b/quic/core/quic_sent_packet_manager.h
index 069ff0f..dac8ccf 100644
--- a/quic/core/quic_sent_packet_manager.h
+++ b/quic/core/quic_sent_packet_manager.h
@@ -52,6 +52,12 @@
   // the packet manager or connection as a result of these callbacks.
   class QUIC_EXPORT_PRIVATE DebugDelegate {
    public:
+    struct QUIC_EXPORT_PRIVATE SendParameters {
+      CongestionControlType congestion_control_type;
+      bool use_pacing;
+      QuicPacketCount initial_congestion_window;
+    };
+
     virtual ~DebugDelegate() {}
 
     // Called when a spurious retransmission is detected.
@@ -84,6 +90,8 @@
                                    int /*new_burst_size*/) {}
 
     virtual void OnOvershootingDetected() {}
+
+    virtual void OnConfigProcessed(const SendParameters& /*parameters*/) {}
   };
 
   // Interface which gets callbacks from the QuicSentPacketManager when