diff --git a/quic/core/http/quic_spdy_stream_test.cc b/quic/core/http/quic_spdy_stream_test.cc
index 60e7430..b6e59a5 100644
--- a/quic/core/http/quic_spdy_stream_test.cc
+++ b/quic/core/http/quic_spdy_stream_test.cc
@@ -1406,17 +1406,17 @@
   session_->OnStreamFrameRetransmitted(frame1);
 
   EXPECT_CALL(*ack_listener1, OnPacketAcked(7, _));
-  EXPECT_TRUE(
-      session_->OnFrameAcked(QuicFrame(frame1), QuicTime::Delta::Zero()));
+  EXPECT_TRUE(session_->OnFrameAcked(QuicFrame(frame1), QuicTime::Delta::Zero(),
+                                     QuicTime::Zero()));
   EXPECT_CALL(*ack_listener1, OnPacketAcked(5, _));
-  EXPECT_TRUE(
-      session_->OnFrameAcked(QuicFrame(frame2), QuicTime::Delta::Zero()));
+  EXPECT_TRUE(session_->OnFrameAcked(QuicFrame(frame2), QuicTime::Delta::Zero(),
+                                     QuicTime::Zero()));
   EXPECT_CALL(*ack_listener2, OnPacketAcked(7, _));
-  EXPECT_TRUE(
-      session_->OnFrameAcked(QuicFrame(frame3), QuicTime::Delta::Zero()));
+  EXPECT_TRUE(session_->OnFrameAcked(QuicFrame(frame3), QuicTime::Delta::Zero(),
+                                     QuicTime::Zero()));
   EXPECT_CALL(*ack_listener2, OnPacketAcked(5, _));
-  EXPECT_TRUE(
-      session_->OnFrameAcked(QuicFrame(frame4), QuicTime::Delta::Zero()));
+  EXPECT_TRUE(session_->OnFrameAcked(QuicFrame(frame4), QuicTime::Delta::Zero(),
+                                     QuicTime::Zero()));
 }
 
 TEST_P(QuicSpdyStreamTest, StreamBecomesZombieWithWriteThatCloses) {
@@ -1631,20 +1631,20 @@
 
   EXPECT_CALL(*mock_ack_listener, OnPacketAcked(body.length(), _));
   QuicStreamFrame frame(stream_->id(), false, 0, header + body);
-  EXPECT_TRUE(
-      session_->OnFrameAcked(QuicFrame(frame), QuicTime::Delta::Zero()));
+  EXPECT_TRUE(session_->OnFrameAcked(QuicFrame(frame), QuicTime::Delta::Zero(),
+                                     QuicTime::Zero()));
 
   EXPECT_CALL(*mock_ack_listener, OnPacketAcked(0, _));
   QuicStreamFrame frame2(stream_->id(), false, (header + body).length(),
                          header2);
-  EXPECT_TRUE(
-      session_->OnFrameAcked(QuicFrame(frame2), QuicTime::Delta::Zero()));
+  EXPECT_TRUE(session_->OnFrameAcked(QuicFrame(frame2), QuicTime::Delta::Zero(),
+                                     QuicTime::Zero()));
 
   EXPECT_CALL(*mock_ack_listener, OnPacketAcked(body2.length(), _));
   QuicStreamFrame frame3(stream_->id(), true,
                          (header + body).length() + header2.length(), body2);
-  EXPECT_TRUE(
-      session_->OnFrameAcked(QuicFrame(frame3), QuicTime::Delta::Zero()));
+  EXPECT_TRUE(session_->OnFrameAcked(QuicFrame(frame3), QuicTime::Delta::Zero(),
+                                     QuicTime::Zero()));
 
   EXPECT_TRUE(
       QuicSpdyStreamPeer::unacked_frame_headers_offsets(stream_).Empty());
@@ -1688,8 +1688,8 @@
               OnPacketAcked(body.length() + body2.length(), _));
   QuicStreamFrame frame(stream_->id(), true, 0,
                         header + body + header2 + body2);
-  EXPECT_TRUE(
-      session_->OnFrameAcked(QuicFrame(frame), QuicTime::Delta::Zero()));
+  EXPECT_TRUE(session_->OnFrameAcked(QuicFrame(frame), QuicTime::Delta::Zero(),
+                                     QuicTime::Zero()));
 
   EXPECT_TRUE(
       QuicSpdyStreamPeer::unacked_frame_headers_offsets(stream_).Empty());
diff --git a/quic/core/quic_sent_packet_manager.cc b/quic/core/quic_sent_packet_manager.cc
index 527f820..204c020 100644
--- a/quic/core/quic_sent_packet_manager.cc
+++ b/quic/core/quic_sent_packet_manager.cc
@@ -610,7 +610,8 @@
 
 void QuicSentPacketManager::MarkPacketHandled(QuicPacketNumber packet_number,
                                               QuicTransmissionInfo* info,
-                                              QuicTime::Delta ack_delay_time) {
+                                              QuicTime::Delta ack_delay_time,
+                                              QuicTime receive_timestamp) {
   QuicPacketNumber newest_transmission =
       GetNewestRetransmission(packet_number, *info);
   // Remove the most recent packet, if it is pending retransmission.
@@ -622,13 +623,14 @@
     const bool fast_path = session_decides_what_to_write() &&
                            info->transmission_type == NOT_RETRANSMISSION;
     if (fast_path) {
-      unacked_packets_.MaybeAggregateAckedStreamFrame(*info, ack_delay_time);
+      unacked_packets_.MaybeAggregateAckedStreamFrame(*info, ack_delay_time,
+                                                      receive_timestamp);
     } else {
       if (session_decides_what_to_write()) {
         unacked_packets_.NotifyAggregatedStreamFrameAcked(ack_delay_time);
       }
-      const bool new_data_acked =
-          unacked_packets_.NotifyFramesAcked(*info, ack_delay_time);
+      const bool new_data_acked = unacked_packets_.NotifyFramesAcked(
+          *info, ack_delay_time, receive_timestamp);
       if (session_decides_what_to_write() && !new_data_acked &&
           info->transmission_type != NOT_RETRANSMISSION) {
         // Record as a spurious retransmission if this packet is a
@@ -651,8 +653,8 @@
     // only handle nullptr encrypted packets in a special way.
     const QuicTransmissionInfo& newest_transmission_info =
         unacked_packets_.GetTransmissionInfo(newest_transmission);
-    unacked_packets_.NotifyFramesAcked(newest_transmission_info,
-                                       ack_delay_time);
+    unacked_packets_.NotifyFramesAcked(newest_transmission_info, ack_delay_time,
+                                       receive_timestamp);
     if (HasCryptoHandshake(newest_transmission_info)) {
       unacked_packets_.RemoveFromInFlight(newest_transmission);
     }
@@ -1241,7 +1243,8 @@
           packet_number_space, acked_packet.packet_number);
     }
     MarkPacketHandled(acked_packet.packet_number, info,
-                      last_ack_frame_.ack_delay_time);
+                      last_ack_frame_.ack_delay_time,
+                      acked_packet.receive_timestamp);
   }
   const bool acked_new_packet = !packets_acked_.empty();
   PostProcessNewlyAckedPackets(last_ack_frame_, ack_receive_time, rtt_updated_,
diff --git a/quic/core/quic_sent_packet_manager.h b/quic/core/quic_sent_packet_manager.h
index 3df874d..787bf8d 100644
--- a/quic/core/quic_sent_packet_manager.h
+++ b/quic/core/quic_sent_packet_manager.h
@@ -481,7 +481,8 @@
   // |info| due to receipt by the peer.
   void MarkPacketHandled(QuicPacketNumber packet_number,
                          QuicTransmissionInfo* info,
-                         QuicTime::Delta ack_delay_time);
+                         QuicTime::Delta ack_delay_time,
+                         QuicTime receive_timestamp);
 
   // Request that |packet_number| be retransmitted after the other pending
   // retransmissions.  Does not add it to the retransmissions if it's already
diff --git a/quic/core/quic_sent_packet_manager_test.cc b/quic/core/quic_sent_packet_manager_test.cc
index c508cca..a0746fe 100644
--- a/quic/core/quic_sent_packet_manager_test.cc
+++ b/quic/core/quic_sent_packet_manager_test.cc
@@ -110,7 +110,7 @@
     EXPECT_CALL(notifier_, HasUnackedCryptoData())
         .WillRepeatedly(Return(false));
     EXPECT_CALL(notifier_, OnStreamFrameRetransmitted(_)).Times(AnyNumber());
-    EXPECT_CALL(notifier_, OnFrameAcked(_, _)).WillRepeatedly(Return(true));
+    EXPECT_CALL(notifier_, OnFrameAcked(_, _, _)).WillRepeatedly(Return(true));
   }
 
   ~QuicSentPacketManagerTest() override {}
@@ -469,7 +469,7 @@
   VerifyRetransmittablePackets(nullptr, 0);
   if (manager_.session_decides_what_to_write()) {
     // Ack 2 causes 2 be considered as spurious retransmission.
-    EXPECT_CALL(notifier_, OnFrameAcked(_, _)).WillOnce(Return(false));
+    EXPECT_CALL(notifier_, OnFrameAcked(_, _, _)).WillOnce(Return(false));
     ExpectAck(2);
     manager_.OnAckFrameStart(QuicPacketNumber(2), QuicTime::Delta::Infinite(),
                              clock_.Now());
@@ -623,7 +623,7 @@
   SendDataPacket(4);
   if (manager_.session_decides_what_to_write()) {
     // No new data gets acked in packet 3.
-    EXPECT_CALL(notifier_, OnFrameAcked(_, _))
+    EXPECT_CALL(notifier_, OnFrameAcked(_, _, _))
         .WillOnce(Return(false))
         .WillRepeatedly(Return(true));
   }
@@ -727,7 +727,7 @@
       // data gets acked.
       ExpectAck(5);
       EXPECT_CALL(*loss_algorithm, DetectLosses(_, _, _, _, _, _));
-      EXPECT_CALL(notifier_, OnFrameAcked(_, _)).WillOnce(Return(false));
+      EXPECT_CALL(notifier_, OnFrameAcked(_, _, _)).WillOnce(Return(false));
       manager_.OnAckFrameStart(QuicPacketNumber(5), QuicTime::Delta::Infinite(),
                                clock_.Now());
       manager_.OnAckRange(QuicPacketNumber(3), QuicPacketNumber(6));
diff --git a/quic/core/quic_session.cc b/quic/core/quic_session.cc
index 89e08ef..9707c34 100644
--- a/quic/core/quic_session.cc
+++ b/quic/core/quic_session.cc
@@ -1582,9 +1582,10 @@
 }
 
 bool QuicSession::OnFrameAcked(const QuicFrame& frame,
-                               QuicTime::Delta ack_delay_time) {
+                               QuicTime::Delta ack_delay_time,
+                               QuicTime receive_timestamp) {
   if (frame.type == MESSAGE_FRAME) {
-    OnMessageAcked(frame.message_frame->message_id);
+    OnMessageAcked(frame.message_frame->message_id, receive_timestamp);
     return true;
   }
   if (frame.type == CRYPTO_FRAME) {
@@ -1839,7 +1840,8 @@
   return {result, 0};
 }
 
-void QuicSession::OnMessageAcked(QuicMessageId message_id) {
+void QuicSession::OnMessageAcked(QuicMessageId message_id,
+                                 QuicTime receive_timestamp) {
   QUIC_DVLOG(1) << ENDPOINT << "message " << message_id << " gets acked.";
 }
 
diff --git a/quic/core/quic_session.h b/quic/core/quic_session.h
index 5988369..32dd680 100644
--- a/quic/core/quic_session.h
+++ b/quic/core/quic_session.h
@@ -142,7 +142,8 @@
 
   // SessionNotifierInterface methods:
   bool OnFrameAcked(const QuicFrame& frame,
-                    QuicTime::Delta ack_delay_time) override;
+                    QuicTime::Delta ack_delay_time,
+                    QuicTime receive_timestamp) override;
   void OnStreamFrameRetransmitted(const QuicStreamFrame& frame) override;
   void OnFrameLost(const QuicFrame& frame) override;
   void RetransmitFrames(const QuicFrames& frames,
@@ -189,7 +190,8 @@
   MessageResult SendMessage(QuicMemSliceSpan message);
 
   // Called when message with |message_id| gets acked.
-  virtual void OnMessageAcked(QuicMessageId message_id);
+  virtual void OnMessageAcked(QuicMessageId message_id,
+                              QuicTime receive_timestamp);
 
   // Called when message with |message_id| is considered as lost.
   virtual void OnMessageLost(QuicMessageId message_id);
diff --git a/quic/core/quic_session_test.cc b/quic/core/quic_session_test.cc
index 4e3228e..c8a0a02 100644
--- a/quic/core/quic_session_test.cc
+++ b/quic/core/quic_session_test.cc
@@ -2209,7 +2209,7 @@
   EXPECT_FALSE(session_.IsFrameOutstanding(QuicFrame(&frame2)));
 
   // message 1 gets acked.
-  session_.OnMessageAcked(1);
+  session_.OnMessageAcked(1, QuicTime::Zero());
   EXPECT_FALSE(session_.IsFrameOutstanding(QuicFrame(&frame)));
 }
 
diff --git a/quic/core/quic_unacked_packet_map.cc b/quic/core/quic_unacked_packet_map.cc
index 1a0b1af..5b3de44 100644
--- a/quic/core/quic_unacked_packet_map.cc
+++ b/quic/core/quic_unacked_packet_map.cc
@@ -407,13 +407,14 @@
 }
 
 bool QuicUnackedPacketMap::NotifyFramesAcked(const QuicTransmissionInfo& info,
-                                             QuicTime::Delta ack_delay) {
+                                             QuicTime::Delta ack_delay,
+                                             QuicTime receive_timestamp) {
   if (session_notifier_ == nullptr) {
     return false;
   }
   bool new_data_acked = false;
   for (const QuicFrame& frame : info.retransmittable_frames) {
-    if (session_notifier_->OnFrameAcked(frame, ack_delay)) {
+    if (session_notifier_->OnFrameAcked(frame, ack_delay, receive_timestamp)) {
       new_data_acked = true;
     }
   }
@@ -436,7 +437,8 @@
 
 void QuicUnackedPacketMap::MaybeAggregateAckedStreamFrame(
     const QuicTransmissionInfo& info,
-    QuicTime::Delta ack_delay) {
+    QuicTime::Delta ack_delay,
+    QuicTime receive_timestamp) {
   if (session_notifier_ == nullptr) {
     return;
   }
@@ -468,7 +470,7 @@
 
     NotifyAggregatedStreamFrameAcked(ack_delay);
     if (frame.type != STREAM_FRAME || frame.stream_frame.fin) {
-      session_notifier_->OnFrameAcked(frame, ack_delay);
+      session_notifier_->OnFrameAcked(frame, ack_delay, receive_timestamp);
       continue;
     }
 
@@ -488,8 +490,11 @@
     // Aggregated stream frame is empty.
     return;
   }
+  // Note: there is no receive_timestamp for an aggregated stream frame.  The
+  // frames that are aggregated may not have been received at the same time.
   session_notifier_->OnFrameAcked(QuicFrame(aggregated_stream_frame_),
-                                  ack_delay);
+                                  ack_delay,
+                                  /*receive_timestamp=*/QuicTime::Zero());
   // Clear aggregated stream frame.
   aggregated_stream_frame_.stream_id = -1;
 }
diff --git a/quic/core/quic_unacked_packet_map.h b/quic/core/quic_unacked_packet_map.h
index 1a37a1f..17589dd 100644
--- a/quic/core/quic_unacked_packet_map.h
+++ b/quic/core/quic_unacked_packet_map.h
@@ -50,7 +50,8 @@
   // Notifies session_notifier that frames have been acked. Returns true if any
   // new data gets acked, returns false otherwise.
   bool NotifyFramesAcked(const QuicTransmissionInfo& info,
-                         QuicTime::Delta ack_delay);
+                         QuicTime::Delta ack_delay,
+                         QuicTime receive_timestamp);
 
   // Notifies session_notifier that frames in |info| are considered as lost.
   void NotifyFramesLost(const QuicTransmissionInfo& info,
@@ -179,7 +180,8 @@
   // frames or control frames, notify the session notifier they get acked
   // immediately.
   void MaybeAggregateAckedStreamFrame(const QuicTransmissionInfo& info,
-                                      QuicTime::Delta ack_delay);
+                                      QuicTime::Delta ack_delay,
+                                      QuicTime receive_timestamp);
 
   // Notify the session notifier of any stream data aggregated in
   // aggregated_stream_frame_.  No effect if the stream frame has an invalid
diff --git a/quic/core/quic_unacked_packet_map_test.cc b/quic/core/quic_unacked_packet_map_test.cc
index 331a0e8..ff26542 100644
--- a/quic/core/quic_unacked_packet_map_test.cc
+++ b/quic/core/quic_unacked_packet_map_test.cc
@@ -551,7 +551,7 @@
 
 TEST_P(QuicUnackedPacketMapTest, AggregateContiguousAckedStreamFrames) {
   testing::InSequence s;
-  EXPECT_CALL(notifier_, OnFrameAcked(_, _)).Times(0);
+  EXPECT_CALL(notifier_, OnFrameAcked(_, _, _)).Times(0);
   unacked_packets_.NotifyAggregatedStreamFrameAcked(QuicTime::Delta::Zero());
 
   QuicTransmissionInfo info1;
@@ -571,20 +571,20 @@
   info4.retransmittable_frames.push_back(QuicFrame(stream_frame4));
 
   // Verify stream frames are aggregated.
-  EXPECT_CALL(notifier_, OnFrameAcked(_, _)).Times(0);
-  unacked_packets_.MaybeAggregateAckedStreamFrame(info1,
-                                                  QuicTime::Delta::Zero());
-  EXPECT_CALL(notifier_, OnFrameAcked(_, _)).Times(0);
-  unacked_packets_.MaybeAggregateAckedStreamFrame(info2,
-                                                  QuicTime::Delta::Zero());
-  EXPECT_CALL(notifier_, OnFrameAcked(_, _)).Times(0);
-  unacked_packets_.MaybeAggregateAckedStreamFrame(info3,
-                                                  QuicTime::Delta::Zero());
+  EXPECT_CALL(notifier_, OnFrameAcked(_, _, _)).Times(0);
+  unacked_packets_.MaybeAggregateAckedStreamFrame(
+      info1, QuicTime::Delta::Zero(), QuicTime::Zero());
+  EXPECT_CALL(notifier_, OnFrameAcked(_, _, _)).Times(0);
+  unacked_packets_.MaybeAggregateAckedStreamFrame(
+      info2, QuicTime::Delta::Zero(), QuicTime::Zero());
+  EXPECT_CALL(notifier_, OnFrameAcked(_, _, _)).Times(0);
+  unacked_packets_.MaybeAggregateAckedStreamFrame(
+      info3, QuicTime::Delta::Zero(), QuicTime::Zero());
 
   // Verify aggregated stream frame gets acked since fin is acked.
-  EXPECT_CALL(notifier_, OnFrameAcked(_, _)).Times(1);
-  unacked_packets_.MaybeAggregateAckedStreamFrame(info4,
-                                                  QuicTime::Delta::Zero());
+  EXPECT_CALL(notifier_, OnFrameAcked(_, _, _)).Times(1);
+  unacked_packets_.MaybeAggregateAckedStreamFrame(
+      info4, QuicTime::Delta::Zero(), QuicTime::Zero());
 }
 
 // Regression test for b/112930090.
@@ -614,17 +614,17 @@
       if (aggregated_stream_frame.data_length + acked_stream_length <=
           kMaxAggregatedDataLength) {
         // Verify the acked stream frame can be aggregated.
-        EXPECT_CALL(notifier_, OnFrameAcked(_, _)).Times(0);
+        EXPECT_CALL(notifier_, OnFrameAcked(_, _, _)).Times(0);
         unacked_packets_.MaybeAggregateAckedStreamFrame(
-            info, QuicTime::Delta::Zero());
+            info, QuicTime::Delta::Zero(), QuicTime::Zero());
         aggregated_data_length += acked_stream_length;
         testing::Mock::VerifyAndClearExpectations(&notifier_);
       } else {
         // Verify the acked stream frame cannot be aggregated because
         // data_length is overflow.
-        EXPECT_CALL(notifier_, OnFrameAcked(_, _)).Times(1);
+        EXPECT_CALL(notifier_, OnFrameAcked(_, _, _)).Times(1);
         unacked_packets_.MaybeAggregateAckedStreamFrame(
-            info, QuicTime::Delta::Zero());
+            info, QuicTime::Delta::Zero(), QuicTime::Zero());
         aggregated_data_length = acked_stream_length;
         testing::Mock::VerifyAndClearExpectations(&notifier_);
       }
@@ -637,9 +637,9 @@
     QuicTransmissionInfo info;
     QuicStreamFrame stream_frame(stream_id, true, offset, acked_stream_length);
     info.retransmittable_frames.push_back(QuicFrame(stream_frame));
-    EXPECT_CALL(notifier_, OnFrameAcked(_, _)).Times(1);
-    unacked_packets_.MaybeAggregateAckedStreamFrame(info,
-                                                    QuicTime::Delta::Zero());
+    EXPECT_CALL(notifier_, OnFrameAcked(_, _, _)).Times(1);
+    unacked_packets_.MaybeAggregateAckedStreamFrame(
+        info, QuicTime::Delta::Zero(), QuicTime::Zero());
     testing::Mock::VerifyAndClearExpectations(&notifier_);
   }
 }
@@ -662,15 +662,15 @@
   info2.retransmittable_frames.push_back(QuicFrame(&go_away));
 
   // Verify 2 contiguous stream frames are aggregated.
-  EXPECT_CALL(notifier_, OnFrameAcked(_, _)).Times(1);
-  unacked_packets_.MaybeAggregateAckedStreamFrame(info1,
-                                                  QuicTime::Delta::Zero());
+  EXPECT_CALL(notifier_, OnFrameAcked(_, _, _)).Times(1);
+  unacked_packets_.MaybeAggregateAckedStreamFrame(
+      info1, QuicTime::Delta::Zero(), QuicTime::Zero());
   // Verify aggregated stream frame gets acked.
-  EXPECT_CALL(notifier_, OnFrameAcked(_, _)).Times(3);
-  unacked_packets_.MaybeAggregateAckedStreamFrame(info2,
-                                                  QuicTime::Delta::Zero());
+  EXPECT_CALL(notifier_, OnFrameAcked(_, _, _)).Times(3);
+  unacked_packets_.MaybeAggregateAckedStreamFrame(
+      info2, QuicTime::Delta::Zero(), QuicTime::Zero());
 
-  EXPECT_CALL(notifier_, OnFrameAcked(_, _)).Times(0);
+  EXPECT_CALL(notifier_, OnFrameAcked(_, _, _)).Times(0);
   unacked_packets_.NotifyAggregatedStreamFrameAcked(QuicTime::Delta::Zero());
 }
 
diff --git a/quic/core/session_notifier_interface.h b/quic/core/session_notifier_interface.h
index 83fc0f1..a601c3e 100644
--- a/quic/core/session_notifier_interface.h
+++ b/quic/core/session_notifier_interface.h
@@ -19,7 +19,8 @@
   // Called when |frame| is acked. Returns true if any new data gets acked,
   // returns false otherwise.
   virtual bool OnFrameAcked(const QuicFrame& frame,
-                            QuicTime::Delta ack_delay_time) = 0;
+                            QuicTime::Delta ack_delay_time,
+                            QuicTime receive_timestamp) = 0;
 
   // Called when |frame| is retransmitted.
   virtual void OnStreamFrameRetransmitted(const QuicStreamFrame& frame) = 0;
diff --git a/quic/quartc/quartc_session.cc b/quic/quartc/quartc_session.cc
index 2e6729c..95c7e86 100644
--- a/quic/quartc/quartc_session.cc
+++ b/quic/quartc/quartc_session.cc
@@ -246,7 +246,8 @@
   session_delegate_->OnMessageReceived(message);
 }
 
-void QuartcSession::OnMessageAcked(QuicMessageId message_id) {
+void QuartcSession::OnMessageAcked(QuicMessageId message_id,
+                                   QuicTime receive_timestamp) {
   auto element = message_to_datagram_id_.find(message_id);
 
   if (element == message_to_datagram_id_.end()) {
@@ -255,6 +256,7 @@
     return;
   }
 
+  // TODO(mellem): Pass receive_timestamp to |delegate_|.
   session_delegate_->OnMessageAcked(/*datagram_id=*/element->second);
 
   // Free up space -- we should never see message_id again.
diff --git a/quic/quartc/quartc_session.h b/quic/quartc/quartc_session.h
index 042827b..cd8d2cb 100644
--- a/quic/quartc/quartc_session.h
+++ b/quic/quartc/quartc_session.h
@@ -176,7 +176,8 @@
   void OnMessageReceived(QuicStringPiece message) override;
 
   // Called when message with |message_id| gets acked.
-  void OnMessageAcked(QuicMessageId message_id) override;
+  void OnMessageAcked(QuicMessageId message_id,
+                      QuicTime receive_timestamp) override;
 
   // Returns number of queued (not sent) messages submitted by
   // SendOrQueueMessage. Messages are queued if connection is congestion
diff --git a/quic/test_tools/quic_test_utils.h b/quic/test_tools/quic_test_utils.h
index bf8edcf..8f1cb7a 100644
--- a/quic/test_tools/quic_test_utils.h
+++ b/quic/test_tools/quic_test_utils.h
@@ -1054,7 +1054,7 @@
   MockSessionNotifier();
   ~MockSessionNotifier() override;
 
-  MOCK_METHOD2(OnFrameAcked, bool(const QuicFrame&, QuicTime::Delta));
+  MOCK_METHOD3(OnFrameAcked, bool(const QuicFrame&, QuicTime::Delta, QuicTime));
   MOCK_METHOD1(OnStreamFrameRetransmitted, void(const QuicStreamFrame&));
   MOCK_METHOD1(OnFrameLost, void(const QuicFrame&));
   MOCK_METHOD2(RetransmitFrames,
diff --git a/quic/test_tools/simple_session_notifier.cc b/quic/test_tools/simple_session_notifier.cc
index e72e0e1..c6e3801 100644
--- a/quic/test_tools/simple_session_notifier.cc
+++ b/quic/test_tools/simple_session_notifier.cc
@@ -135,7 +135,8 @@
     QuicStreamFrame stream_frame(
         QuicUtils::GetCryptoStreamId(connection_->transport_version()), false,
         interval.min(), interval.max() - interval.min());
-    OnFrameAcked(QuicFrame(stream_frame), QuicTime::Delta::Zero());
+    OnFrameAcked(QuicFrame(stream_frame), QuicTime::Delta::Zero(),
+                 QuicTime::Zero());
   }
 }
 
@@ -202,7 +203,8 @@
 }
 
 bool SimpleSessionNotifier::OnFrameAcked(const QuicFrame& frame,
-                                         QuicTime::Delta /*ack_delay_time*/) {
+                                         QuicTime::Delta /*ack_delay_time*/,
+                                         QuicTime /*receive_timestamp*/) {
   QUIC_DVLOG(1) << "Acking " << frame;
   if (frame.type == CRYPTO_FRAME) {
     StreamState* state = &crypto_state_[frame.crypto_frame->level];
diff --git a/quic/test_tools/simple_session_notifier.h b/quic/test_tools/simple_session_notifier.h
index e7d4fdc..25c9941 100644
--- a/quic/test_tools/simple_session_notifier.h
+++ b/quic/test_tools/simple_session_notifier.h
@@ -65,7 +65,8 @@
 
   // SessionNotifierInterface methods:
   bool OnFrameAcked(const QuicFrame& frame,
-                    QuicTime::Delta ack_delay_time) override;
+                    QuicTime::Delta ack_delay_time,
+                    QuicTime receive_timestamp) override;
   void OnStreamFrameRetransmitted(const QuicStreamFrame& frame) override {}
   void OnFrameLost(const QuicFrame& frame) override;
   void RetransmitFrames(const QuicFrames& frames,
diff --git a/quic/test_tools/simple_session_notifier_test.cc b/quic/test_tools/simple_session_notifier_test.cc
index d2aad9f..d9958c8 100644
--- a/quic/test_tools/simple_session_notifier_test.cc
+++ b/quic/test_tools/simple_session_notifier_test.cc
@@ -154,7 +154,8 @@
   QuicStreamFrame stream_frame(
       QuicUtils::GetCryptoStreamId(connection_.transport_version()), false,
       1024, 1024);
-  notifier_.OnFrameAcked(QuicFrame(stream_frame), QuicTime::Delta::Zero());
+  notifier_.OnFrameAcked(QuicFrame(stream_frame), QuicTime::Delta::Zero(),
+                         QuicTime::Zero());
   EXPECT_TRUE(notifier_.StreamIsWaitingForAcks(
       QuicUtils::GetCryptoStreamId(connection_.transport_version())));
   // Neuters unencrypted data.
@@ -315,8 +316,10 @@
   // Ack stream 3 [3, 7), and stream 5 [8, 10).
   QuicStreamFrame ack_frame1(3, false, 3, 4);
   QuicStreamFrame ack_frame2(5, false, 8, 2);
-  notifier_.OnFrameAcked(QuicFrame(ack_frame1), QuicTime::Delta::Zero());
-  notifier_.OnFrameAcked(QuicFrame(ack_frame2), QuicTime::Delta::Zero());
+  notifier_.OnFrameAcked(QuicFrame(ack_frame1), QuicTime::Delta::Zero(),
+                         QuicTime::Zero());
+  notifier_.OnFrameAcked(QuicFrame(ack_frame2), QuicTime::Delta::Zero(),
+                         QuicTime::Zero());
   EXPECT_FALSE(notifier_.WillingToWrite());
 
   // Force to send.
diff --git a/quic/test_tools/simulator/quic_endpoint.cc b/quic/test_tools/simulator/quic_endpoint.cc
index 043eae9..78cc302 100644
--- a/quic/test_tools/simulator/quic_endpoint.cc
+++ b/quic/test_tools/simulator/quic_endpoint.cc
@@ -265,9 +265,10 @@
 }
 
 bool QuicEndpoint::OnFrameAcked(const QuicFrame& frame,
-                                QuicTime::Delta ack_delay_time) {
+                                QuicTime::Delta ack_delay_time,
+                                QuicTime receive_timestamp) {
   if (notifier_ != nullptr) {
-    return notifier_->OnFrameAcked(frame, ack_delay_time);
+    return notifier_->OnFrameAcked(frame, ack_delay_time, receive_timestamp);
   }
   return false;
 }
diff --git a/quic/test_tools/simulator/quic_endpoint.h b/quic/test_tools/simulator/quic_endpoint.h
index 8bbdbd7..8efef0e 100644
--- a/quic/test_tools/simulator/quic_endpoint.h
+++ b/quic/test_tools/simulator/quic_endpoint.h
@@ -122,7 +122,8 @@
 
   // Begin SessionNotifierInterface methods:
   bool OnFrameAcked(const QuicFrame& frame,
-                    QuicTime::Delta ack_delay_time) override;
+                    QuicTime::Delta ack_delay_time,
+                    QuicTime receive_timestamp) override;
   void OnStreamFrameRetransmitted(const QuicStreamFrame& frame) override {}
   void OnFrameLost(const QuicFrame& frame) override;
   void RetransmitFrames(const QuicFrames& frames,