gfe-relnote: Default-initialize QUIC BBRv2's inflight_hi_headroom from flags. No behavior change.

PiperOrigin-RevId: 271996677
Change-Id: Idf3c84905c7761ba30efac90a1729f7e0e996a3f

quic/core/congestion_control/bbr2_misc.h

diff --git a/quic/core/congestion_control/bbr2_misc.h b/quic/core/congestion_control/bbr2_misc.h
index bf2c00d..d5b2742 100644
--- a/quic/core/congestion_control/bbr2_misc.h
+++ b/quic/core/congestion_control/bbr2_misc.h
@@ -145,7 +145,8 @@
   QuicRoundTripCount initial_max_ack_height_filter_window = 10;
 
   // Fraction of unutilized headroom to try to leave in path upon high loss.
-  float inflight_hi_headroom = 0.15;
+  float inflight_hi_headroom =
+      GetQuicFlag(FLAGS_quic_bbr2_default_inflight_hi_headroom);
 
   // Estimate startup/bw probing has gone too far if loss rate exceeds this.
   float loss_threshold = GetQuicFlag(FLAGS_quic_bbr2_default_loss_threshold);