Don't copy the QuicAckFrame into the QuicPacketGenerator. Protected by quic_dont_copy_acks.

net/quic/quic_packet_generator.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/quic/quic_packet_generator.h"
 
 #include "base/logging.h"
 #include "net/quic/quic_bug_tracker.h"
 #include "net/quic/quic_flags.h"
 #include "net/quic/quic_utils.h"
@@ skipping 180 matching lines @@
 }
 
 void QuicPacketGenerator::FlushAllQueuedFrames() {
   SendQueuedFrames(/*flush=*/true);
 }
 
 bool QuicPacketGenerator::HasQueuedFrames() const {
   return packet_creator_.HasPendingFrames() || HasPendingFrames();
 }
 
+bool QuicPacketGenerator::IsPendingPacketEmpty() const {
+  return !packet_creator_.HasPendingFrames();
+}
+
 bool QuicPacketGenerator::HasPendingFrames() const {
   return should_send_ack_ || should_send_stop_waiting_ ||
          !queued_control_frames_.empty();
 }
 
 bool QuicPacketGenerator::AddNextPendingFrame() {
   if (should_send_ack_) {
-    delegate_->PopulateAckFrame(&pending_ack_frame_);
-    // If we can't this add the frame now, then we still need to do so later.
-    should_send_ack_ =
-        !packet_creator_.AddSavedFrame(QuicFrame(&pending_ack_frame_));
-    // Return success if we have cleared out this flag (i.e., added the frame).
-    // If we still need to send, then the frame is full, and we have failed.
+    if (FLAGS_quic_dont_copy_acks) {
+      should_send_ack_ =
+          !packet_creator_.AddSavedFrame(delegate_->GetUpdatedAckFrame());
+    } else {
+      delegate_->PopulateAckFrame(&pending_ack_frame_);
+      // If we can't this add the frame now, then we still need to do so later.
+      should_send_ack_ =
+          !packet_creator_.AddSavedFrame(QuicFrame(&pending_ack_frame_));
+      // Return success if we have added the frame.
+    }
     return !should_send_ack_;
   }
 
   if (should_send_stop_waiting_) {
     delegate_->PopulateStopWaitingFrame(&pending_stop_waiting_frame_);
     // If we can't this add the frame now, then we still need to do so later.
     should_send_stop_waiting_ =
         !packet_creator_.AddSavedFrame(QuicFrame(&pending_stop_waiting_frame_));
     // Return success if we have cleared out this flag (i.e., added the frame).
     // If we still need to send, then the frame is full, and we have failed.
@@ skipping 69 matching lines @@
 
 void QuicPacketGenerator::SetCurrentPath(
     QuicPathId path_id,
     QuicPacketNumber least_packet_awaited_by_peer,
     QuicPacketCount max_packets_in_flight) {
   packet_creator_.SetCurrentPath(path_id, least_packet_awaited_by_peer,
                                  max_packets_in_flight);
 }
 
 }  // namespace net