Reduce a LOG(WARNING) to a DLOG(WARNING).

net/quic/quic_connection.cc

Index: net/quic/quic_connection.cc
diff --git a/net/quic/quic_connection.cc b/net/quic/quic_connection.cc
index 31beab4841bb2dee470ff6125fc3108496a2702c..957cc3994adf410456fc423cb4d5764bcd337b4c 100644
--- a/net/quic/quic_connection.cc
+++ b/net/quic/quic_connection.cc
@@ -829,9 +829,9 @@ bool QuicConnection::OnPingFrame(const QuicPingFrame& frame) {
 
 const char* QuicConnection::ValidateAckFrame(const QuicAckFrame& incoming_ack) {
   if (incoming_ack.largest_observed > packet_generator_.packet_number()) {
-    LOG(WARNING) << ENDPOINT << "Peer's observed unsent packet:"
-                 << incoming_ack.largest_observed << " vs "
-                 << packet_generator_.packet_number();
+    DLOG(WARNING) << ENDPOINT << "Peer's observed unsent packet:"
+                  << incoming_ack.largest_observed << " vs "
+                  << packet_generator_.packet_number();
     // We got an error for data we have not sent.  Error out.
     return "Largest observed too high.";
   }