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

net/quic/quic_connection_test.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_connection.h"
 
 #include <ostream>
 
 #include "base/bind.h"
 #include "base/macros.h"
@@ skipping 681 matching lines @@
         .WillRepeatedly(Return(QuicTime::Zero()));
     EXPECT_CALL(*loss_algorithm_, DetectLosses(_, _, _, _)).Times(AnyNumber());
     // TODO(ianswett): Fix QuicConnectionTests so they don't attempt to write
     // non-crypto stream data at ENCRYPTION_NONE.
     FLAGS_quic_never_write_unencrypted_data = false;
   }
 
   QuicVersion version() { return GetParam().version; }
 
   QuicAckFrame* outgoing_ack() {
-    QuicConnectionPeer::PopulateAckFrame(&connection_, &ack_);
+    if (FLAGS_quic_dont_copy_acks) {
+      QuicFrame ack_frame =
+          QuicConnectionPeer::GetUpdatedAckFrame(&connection_);
+      ack_ = *ack_frame.ack_frame;
+    } else {
+      QuicConnectionPeer::PopulateAckFrame(&connection_, &ack_);
+    }
     return &ack_;
   }
 
   QuicStopWaitingFrame* stop_waiting() {
     QuicConnectionPeer::PopulateStopWaitingFrame(&connection_, &stop_waiting_);
     return &stop_waiting_;
   }
 
   QuicPacketNumber least_unacked() {
     if (writer_->stop_waiting_frames().empty()) {
@@ skipping 3984 matching lines @@
   // result in multiple attempts to close the connection - it will be marked as
   // disconnected after the first call.
   EXPECT_CALL(visitor_, OnConnectionClosed(_, _)).Times(1);
   connection_.SendConnectionCloseWithDetails(QUIC_NO_ERROR, "no reason");
   connection_.SendConnectionCloseWithDetails(QUIC_NO_ERROR, "no reason");
 }
 
 }  // namespace
 }  // namespace test
 }  // namespace net