Keep an instance of QuicAckFrame in QuicConnection in order to reduce

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 ddeb4677f00b1f880a6a6c1a6185be892e9aa9e6..e944aea51951a473b7b1dafc5f6bc21e86a2dbb2 100644
--- a/net/quic/quic_connection.h
+++ b/net/quic/quic_connection.h
@@ -370,8 +370,8 @@ class NET_EXPORT_PRIVATE QuicConnection
   bool ShouldGeneratePacket(TransmissionType transmission_type,
                             HasRetransmittableData retransmittable,
                             IsHandshake handshake) override;
-  QuicAckFrame* CreateAckFrame() override;
-  QuicStopWaitingFrame* CreateStopWaitingFrame() override;
+  void PopulateAckFrame(QuicAckFrame* ack) override;
+  void PopulateStopWaitingFrame(QuicStopWaitingFrame* stop_waiting) override;
   void OnSerializedPacket(const SerializedPacket& packet) override;
 
   // QuicSentPacketManager::NetworkChangeVisitor
@@ -629,9 +629,6 @@ class NET_EXPORT_PRIVATE QuicConnection
 
   void ProcessStopWaitingFrame(const QuicStopWaitingFrame& stop_waiting);
 
-  // Update |stop_waiting| for an outgoing ack.
-  void UpdateStopWaiting(QuicStopWaitingFrame* stop_waiting);
-
   // Queues an ack or sets the ack alarm when an incoming packet arrives that
   // should be acked.
   void MaybeQueueAck();