Remove largest_observed_ from QuicSentPacketManager, since it's also in

net/quic/quic_unacked_packet_map.h

Index: net/quic/quic_unacked_packet_map.h
diff --git a/net/quic/quic_unacked_packet_map.h b/net/quic/quic_unacked_packet_map.h
index 0684b4db9f74407792f77edfa997e7514604a16b..3c367f6e670c61892f5c9fc6270bf8f7de24df44 100644
--- a/net/quic/quic_unacked_packet_map.h
+++ b/net/quic/quic_unacked_packet_map.h
@@ -59,6 +59,11 @@ class NET_EXPORT_PRIVATE QuicUnackedPacketMap {
     return largest_sent_packet_;
   }
 
+  // Returns the largest sequence number that has been acked.
+  QuicPacketSequenceNumber largest_observed() const {
+    return largest_observed_;
+  }
+
   // Returns the sum of bytes from all packets in flight.
   QuicByteCount bytes_in_flight() const {
     return bytes_in_flight_;