Add a new QUIC Ack Decimation mode that is reordering tolerant. Protected by FLAG_quic_ack_decimati…

net/quic/quic_connection.h

Index: net/quic/quic_connection.h
diff --git a/net/quic/quic_connection.h b/net/quic/quic_connection.h
index df649b594630b6574f1aabe3f28ff722cfeddb41..72f0272173680a77dd7838e47cd5090735f22359 100644
--- a/net/quic/quic_connection.h
+++ b/net/quic/quic_connection.h
@@ -307,6 +307,8 @@ class NET_EXPORT_PRIVATE QuicConnection
     BUNDLE_PENDING_ACK = 2,
   };
 
+  enum AckMode { TCP_ACKING, ACK_DECIMATION, ACK_DECIMATION_WITH_REORDERING };
+
   // Constructs a new QuicConnection for |connection_id| and |address| using
   // |writer| to write packets. |owns_writer| specifies whether the connection
   // takes ownership of |writer|. |helper| must outlive this connection.
@@ -919,13 +921,15 @@ class NET_EXPORT_PRIVATE QuicConnection
   bool ack_queued_;
   // How many retransmittable packets have arrived without sending an ack.
   QuicPacketCount num_retransmittable_packets_received_since_last_ack_sent_;
+  // Whether there were missing packets in the last sent ack.
+  bool last_ack_had_missing_packets_;
   // How many consecutive packets have arrived without sending an ack.
   QuicPacketCount num_packets_received_since_last_ack_sent_;
   // Indicates how many consecutive times an ack has arrived which indicates
   // the peer needs to stop waiting for some packets.
   int stop_waiting_count_;
-  // When true, ack only every 10 packets as long as they arrive close together.
-  bool ack_decimation_enabled_;
+  // Indicates the current ack mode, defaults to acking every 2 packets.
+  AckMode ack_mode_;
 
   // Indicates the retransmit alarm is going to be set by the
   // ScopedRetransmitAlarmDelayer