Default to BBR congestion control for QUIC. Protected by

net/quic/core/quic_sent_packet_manager.cc

Index: net/quic/core/quic_sent_packet_manager.cc
diff --git a/net/quic/core/quic_sent_packet_manager.cc b/net/quic/core/quic_sent_packet_manager.cc
index 2841075baa1faec30d24a0dc4974ef2b6dd36b06..7233e5212a2db5d031dd619a6ed0a15123ec8dcf 100644
--- a/net/quic/core/quic_sent_packet_manager.cc
+++ b/net/quic/core/quic_sent_packet_manager.cc
@@ -117,6 +117,9 @@ void QuicSentPacketManager::SetFromConfig(const QuicConfig& config) {
     }
   } else if (config.HasClientRequestedIndependentOption(kBYTE, perspective_)) {
     SetSendAlgorithm(kCubic);
+  } else if (FLAGS_quic_reloadable_flag_quic_default_to_bbr &&
+             config.HasClientRequestedIndependentOption(kQBIC, perspective_)) {
+    SetSendAlgorithm(kCubicBytes);
   } else if (FLAGS_quic_reloadable_flag_quic_enable_pcc &&
              config.HasClientRequestedIndependentOption(kTPCC, perspective_)) {
     SetSendAlgorithm(kPCC);