Add more detailed logging to QUIC's ack validation. No functional change.

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 f9cce7e27f88f80a89a164c2db0f5cca3cb7c58f..9525b266d87b9cec5be23a3ef3c96eca9efc0d1b 100644
--- a/net/quic/quic_connection.cc
+++ b/net/quic/quic_connection.cc
@@ -767,7 +767,10 @@ const char* QuicConnection::ValidateAckFrame(const QuicAckFrame& incoming_ack) {
   if (incoming_ack.largest_observed < sent_packet_manager_.largest_observed()) {
     LOG(WARNING) << ENDPOINT << "Peer's largest_observed packet decreased:"
                  << incoming_ack.largest_observed << " vs "
-                 << sent_packet_manager_.largest_observed();
+                 << sent_packet_manager_.largest_observed()
+                 << " packet_number:" << last_header_.packet_number
+                 << " largest seen with ack:" << largest_seen_packet_with_ack_
+                 << " connection_id: " << connection_id_;
     // A new ack has a diminished largest_observed value.  Error out.
     // If this was an old packet, we wouldn't even have checked.
     return "Largest observed too low";