Move quic_flags.h from net/quic/core to net/quic/platform and split into api and impl.

net/quic/core/congestion_control/bbr_sender_test.cc

Index: net/quic/core/congestion_control/bbr_sender_test.cc
diff --git a/net/quic/core/congestion_control/bbr_sender_test.cc b/net/quic/core/congestion_control/bbr_sender_test.cc
index 1923f930539485671cca7f6f2e0fabcf3938c2aa..f89c8ad8944470dafd3e9403ec6a632ad95693ec 100644
--- a/net/quic/core/congestion_control/bbr_sender_test.cc
+++ b/net/quic/core/congestion_control/bbr_sender_test.cc
@@ -348,7 +348,7 @@ TEST_F(BbrSenderTest, SimpleTransfer2RTTAggregationKeepSending) {
 TEST_F(BbrSenderTest, SimpleTransferAckDecimation) {
   FLAGS_quic_reloadable_flag_quic_bbr_ack_aggregation_bytes = true;
   // Decrease the CWND gain so extra CWND is required with stretch acks.
-  base::SetFlag(&FLAGS_quic_bbr_cwnd_gain, 1.0);
+  SetQuicFlag(&FLAGS_quic_bbr_cwnd_gain, 1.0);
   sender_ = new BbrSender(
       rtt_stats_,
       QuicSentPacketManagerPeer::GetUnackedPacketMap(
@@ -385,7 +385,7 @@ TEST_F(BbrSenderTest, SimpleTransferAckDecimationKeepSending) {
   FLAGS_quic_reloadable_flag_quic_bbr_add_tso_cwnd = true;
   FLAGS_quic_reloadable_flag_quic_bbr_keep_sending_at_recent_rate = true;
   // Decrease the CWND gain so extra CWND is required with stretch acks.
-  base::SetFlag(&FLAGS_quic_bbr_cwnd_gain, 1.0);
+  SetQuicFlag(&FLAGS_quic_bbr_cwnd_gain, 1.0);
   sender_ = new BbrSender(
       rtt_stats_,
       QuicSentPacketManagerPeer::GetUnackedPacketMap(