Move headers stream from 0 to 60 in v99

This CL also fixes a few tests that were incorrectly using the headers stream.

gfe-relnote: change header stream number, protected by v99 flag
PiperOrigin-RevId: 253691890
Change-Id: I1351cad387871efe39fb4387eac546e9a24efb7c
diff --git a/quic/test_tools/quic_test_utils.cc b/quic/test_tools/quic_test_utils.cc
index 38873dd..100f4e9 100644
--- a/quic/test_tools/quic_test_utils.cc
+++ b/quic/test_tools/quic_test_utils.cc
@@ -1147,10 +1147,13 @@
 QuicStreamId GetNthClientInitiatedBidirectionalStreamId(
     QuicTransportVersion version,
     int n) {
+  int num = n;
+  if (!VersionLacksHeadersStream(version)) {
+    num++;  // + 1 because spdy_session contains headers stream.
+  }
   return QuicUtils::GetFirstBidirectionalStreamId(version,
                                                   Perspective::IS_CLIENT) +
-         // + 1 because spdy_session contains headers stream.
-         QuicUtils::StreamIdDelta(version) * (n + 1);
+         QuicUtils::StreamIdDelta(version) * num;
 }
 
 QuicStreamId GetNthServerInitiatedBidirectionalStreamId(