Update from https://crrev.com/316786

net/quic/quic_ack_notifier_manager.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_QUIC_QUIC_ACK_NOTIFIER_MANAGER_H_
 #define NET_QUIC_QUIC_ACK_NOTIFIER_MANAGER_H_
 
 #include <list>
 #include <map>
 
@@ skipping 30 matching lines @@
 
   // This is called after a packet has been serialized, is ready to be sent, and
   // contains retransmittable frames (which may have associated AckNotifiers).
   // If any of the retransmittable frames included in |serialized_packet| have
   // AckNotifiers registered, then add them to our internal map and additionally
   // inform the AckNotifier of the sequence number which it should track.
   void OnSerializedPacket(const SerializedPacket& serialized_packet);
 
  private:
   typedef std::list<QuicAckNotifier*> AckNotifierList;
-  typedef base::hash_set<QuicAckNotifier*> AckNotifierSet;
   // TODO(ianswett): Further improvement may come from changing this to a deque.
   typedef base::hash_map<QuicPacketSequenceNumber, AckNotifierList>
       AckNotifierMap;
 
-  // On every ACK frame received by the connection, all the ack_notifiers_ will
-  // be told which sequeunce numbers were ACKed.
-  // Once a given QuicAckNotifier has seen all the sequence numbers it is
-  // interested in, it will be deleted, and removed from this set.
-  // Owns the AckNotifiers in this set.
-  AckNotifierSet ack_notifiers_;
-
   // Maps from sequence number to the AckNotifiers which are registered
   // for that sequence number. On receipt of an ACK for a given sequence
   // number, call OnAck for all mapped AckNotifiers.
-  // Does not own the AckNotifiers.
+  // When the last reference is removed from the map, the notifier is deleted.
   AckNotifierMap ack_notifier_map_;
 
   DISALLOW_COPY_AND_ASSIGN(AckNotifierManager);
 };
 
 }  // namespace net
 
 #endif  // NET_QUIC_QUIC_ACK_NOTIFIER_MANAGER_H_