Add a MASQUE debug log

PiperOrigin-RevId: 361274079
Change-Id: I7ab39ddc446880bedd913632946ebc4382416ca1
diff --git a/quic/masque/masque_client_session.cc b/quic/masque/masque_client_session.cc
index ccbe32a..8793d53 100644
--- a/quic/masque/masque_client_session.cc
+++ b/quic/masque/masque_client_session.cc
@@ -95,6 +95,10 @@
 
   QuicDatagramFlowId flow_id = GetNextDatagramFlowId();
 
+  QUIC_DLOG(INFO) << "Sending CONNECT-UDP request for " << target_server_address
+                  << " using flow ID " << flow_id << " on stream "
+                  << stream->id();
+
   // Send the request.
   spdy::Http2HeaderBlock headers;
   headers[":method"] = "CONNECT-UDP";