Modify write_index_ advancement to incorporate coalescing stream frames.

gfe-relnote: protected by gfe2_restart_flag_quic_coalesce_stream_frames_2
PiperOrigin-RevId: 279803164
Change-Id: Idc809c831725b92401b2fd5864379398ddec1bf0
diff --git a/quic/core/quic_packet_creator_test.cc b/quic/core/quic_packet_creator_test.cc
index 1b7deda..da6b5ea 100644
--- a/quic/core/quic_packet_creator_test.cc
+++ b/quic/core/quic_packet_creator_test.cc
@@ -1999,7 +1999,7 @@
   if (!GetParam().version_serialization) {
     creator_.StopSendingVersion();
   }
-  SetQuicReloadableFlag(quic_coalesce_stream_frames, true);
+  SetQuicRestartFlag(quic_coalesce_stream_frames_2, true);
   const size_t max_plaintext_size =
       client_framer_.GetMaxPlaintextSize(creator_.max_packet_length());
   EXPECT_FALSE(creator_.HasPendingFrames());