Handle receive timestamps properly when overestimate avoidance (kBSAO) is enabled

I originally hoped we could just remove BSAO code after shipping timestamps; however, this is straightforward to implement, and removes a potential edge case.

PiperOrigin-RevId: 984021496

quiche/quic/core/congestion_control/bandwidth_sampler.cc

diff --git a/quiche/quic/core/congestion_control/bandwidth_sampler.cc b/quiche/quic/core/congestion_control/bandwidth_sampler.cc
index 9cbb714..82e9791 100644
--- a/quiche/quic/core/congestion_control/bandwidth_sampler.cc
+++ b/quiche/quic/core/congestion_control/bandwidth_sampler.cc
@@ -200,7 +200,8 @@
     last_acked_packet_receive_time_ = QuicTime::Zero();
     if (overestimate_avoidance_) {
       recent_ack_points_.Clear();
-      recent_ack_points_.Update(sent_time, total_bytes_acked_);
+      recent_ack_points_.Update(sent_time, QuicTime::Zero(),
+                                total_bytes_acked_);
       a0_candidates_.clear();
       a0_candidates_.push_back(recent_ack_points_.MostRecentPoint());
     }
@@ -399,10 +400,8 @@
   last_acked_packet_ack_time_ = ack_time;
   last_acked_packet_receive_time_ = acked_packet.receive_timestamp;
   if (overestimate_avoidance_) {
-    // Note that this does not store `receive_timestamp`.  Ideally, the receive
-    // timestamps prove sufficiently useful in dealing with overestimation that
-    // we can eventually remove `overestimate_avoidance_` altogether.
-    recent_ack_points_.Update(ack_time, total_bytes_acked_);
+    recent_ack_points_.Update(ack_time, acked_packet.receive_timestamp,
+                              total_bytes_acked_);
   }
 
   if (is_app_limited_) {

quiche/quic/core/congestion_control/bandwidth_sampler.h

diff --git a/quiche/quic/core/congestion_control/bandwidth_sampler.h b/quiche/quic/core/congestion_control/bandwidth_sampler.h
index 2b7d705..d8f433b 100644
--- a/quiche/quic/core/congestion_control/bandwidth_sampler.h
+++ b/quiche/quic/core/congestion_control/bandwidth_sampler.h
@@ -410,7 +410,8 @@
   // RecentAckPoints maintains the most recent 2 ack points at distinct times.
   class QUICHE_EXPORT RecentAckPoints {
    public:
-    void Update(QuicTime ack_time, QuicByteCount total_bytes_acked) {
+    void Update(QuicTime ack_time, QuicTime receive_time,
+                QuicByteCount total_bytes_acked) {
       QUICHE_DCHECK_GE(total_bytes_acked, ack_points_[1].total_bytes_acked);
 
       if (ack_time < ack_points_[1].ack_time) {
@@ -423,6 +424,7 @@
         ack_points_[1].ack_time = ack_time;
       }
 
+      ack_points_[1].receive_time = receive_time;
       ack_points_[1].total_bytes_acked = total_bytes_acked;
     }
 

quiche/quic/core/congestion_control/bandwidth_sampler_test.cc

diff --git a/quiche/quic/core/congestion_control/bandwidth_sampler_test.cc b/quiche/quic/core/congestion_control/bandwidth_sampler_test.cc
index 8bc491b..2a34327 100644
--- a/quiche/quic/core/congestion_control/bandwidth_sampler_test.cc
+++ b/quiche/quic/core/congestion_control/bandwidth_sampler_test.cc
@@ -921,11 +921,6 @@
 }
 
 TEST_P(BandwidthSamplerTest, ReceiveTimestamps) {
-  if (GetParam().overestimate_avoidance) {
-    // Receive timestamps are not used when overestimate avoidance is on.
-    GTEST_SKIP();
-  }
-
   constexpr QuicTimeDelta kTimeBetweenPackets =
       QuicTimeDelta::FromMilliseconds(10);
   constexpr QuicBandwidth kExpectedBandwidth =