gfe-relnote: Add an IsAckFrameEmpty const method to received_packet_manager and make sure GetUpdatedAckFrame is only called to retrieve nonempty ACK frame. Refactoring only, not protected.

PiperOrigin-RevId: 296026015
Change-Id: I41976873d68db37b5c276befd3330c9cbda00108
diff --git a/quic/core/uber_received_packet_manager.h b/quic/core/uber_received_packet_manager.h
index 14ba868..d76ce13 100644
--- a/quic/core/uber_received_packet_manager.h
+++ b/quic/core/uber_received_packet_manager.h
@@ -70,6 +70,9 @@
   // Get the earliest ack_timeout of all packet number spaces.
   QuicTime GetEarliestAckTimeout() const;
 
+  // Return true if ack frame of |packet_number_space| is empty.
+  bool IsAckFrameEmpty(PacketNumberSpace packet_number_space) const;
+
   QuicPacketNumber peer_least_packet_awaiting_ack() const;
 
   size_t min_received_before_ack_decimation() const;