Add DCHECK to ensure OnConnectionMigration is only called on the server.

PiperOrigin-RevId: 893071056

quiche/quic/core/quic_connection.cc

diff --git a/quiche/quic/core/quic_connection.cc b/quiche/quic/core/quic_connection.cc
index 18619fd..a700d08 100644
--- a/quiche/quic/core/quic_connection.cc
+++ b/quiche/quic/core/quic_connection.cc
@@ -5618,6 +5618,7 @@
 }
 
 void QuicConnection::OnConnectionMigration() {
+  QUICHE_DCHECK_EQ(perspective_, Perspective::IS_SERVER);
   if (debug_visitor_ != nullptr) {
     const QuicTime now = clock_->ApproximateNow();
     if (now >= stats_.handshake_completion_time) {