Change some of QUIC's AckNotifier datastructures from maps to hashmaps

net/quic/quic_ack_notifier_manager.h

Index: net/quic/quic_ack_notifier_manager.h
diff --git a/net/quic/quic_ack_notifier_manager.h b/net/quic/quic_ack_notifier_manager.h
index 122bda1521f2ee0de2470fcd595f04e1e8909aaf..4fc8b3d5403545dd6537d5e81e5ea56a58865045 100644
--- a/net/quic/quic_ack_notifier_manager.h
+++ b/net/quic/quic_ack_notifier_manager.h
@@ -5,6 +5,7 @@
 #ifndef NET_QUIC_QUIC_ACK_NOTIFIER_MANAGER_H_
 #define NET_QUIC_QUIC_ACK_NOTIFIER_MANAGER_H_
 
+#include <list>
 #include <map>
 
 #include "base/containers/hash_tables.h"
@@ -45,8 +46,11 @@ class NET_EXPORT_PRIVATE AckNotifierManager {
   void OnSerializedPacket(const SerializedPacket& serialized_packet);
 
  private:
+  typedef std::list<QuicAckNotifier*> AckNotifierList;
   typedef base::hash_set<QuicAckNotifier*> AckNotifierSet;
-  typedef std::map<QuicPacketSequenceNumber, AckNotifierSet> AckNotifierMap;
+  // 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.