Log more info on any pending frames/bytes right before address update in connection migration.

PiperOrigin-RevId: 396949466

quic/core/quic_connection.cc

diff --git a/quic/core/quic_connection.cc b/quic/core/quic_connection.cc
index 4617e8c..4e48912 100644
--- a/quic/core/quic_connection.cc
+++ b/quic/core/quic_connection.cc
@@ -5355,6 +5355,17 @@
           std::move(alternative_path_.rtt_stats).value());
     }
   }
+  if (packet_creator_.HasPendingFrames() ||
+      packet_creator_.pending_padding_bytes() > 0) {
+    QUIC_BUG(quic_bug_5196)
+        << "Starts effective peer migration with pending frame types: "
+        << packet_creator_.GetPendingFramesInfo() << ". pending_padding_bytes: "
+        << packet_creator_.pending_padding_bytes()
+        << ". Address change type is " << AddressChangeTypeToString(type)
+        << ". Current frame type: " << framer_.current_received_frame_type()
+        << ". Previous frame type: "
+        << framer_.previously_received_frame_type();
+  }
   // Update to the new peer address.
   UpdatePeerAddress(last_received_packet_info_.source_address);
   // Update the default path.