Create scaffolding for experimenting with PCC. Protected by FLAGS_quic_reloadable_flag_quic_enable…

net/quic/core/congestion_control/send_algorithm_interface.cc

Index: net/quic/core/congestion_control/send_algorithm_interface.cc
diff --git a/net/quic/core/congestion_control/send_algorithm_interface.cc b/net/quic/core/congestion_control/send_algorithm_interface.cc
index 75bf7441ab2dae9ac63bad6e5d40f0544516837b..385d46eda137b9865a19433f476b0164bc3efa54 100644
--- a/net/quic/core/congestion_control/send_algorithm_interface.cc
+++ b/net/quic/core/congestion_control/send_algorithm_interface.cc
@@ -9,7 +9,9 @@
 #include "net/quic/core/congestion_control/tcp_cubic_sender_packets.h"
 #include "net/quic/core/quic_packets.h"
 #include "net/quic/platform/api/quic_bug_tracker.h"
+#include "net/quic/platform/api/quic_flag_utils.h"
 #include "net/quic/platform/api/quic_flags.h"
+#include "net/quic/platform/api/quic_pcc_sender.h"
 
 namespace net {
 
@@ -35,7 +37,13 @@ SendAlgorithmInterface* SendAlgorithmInterface::Create(
     // Fall back to CUBIC if BBR is disabled.
     // FALLTHROUGH_INTENDED
     case kPCC:
-    // Fall back to CUBIC if no PCC implementation.
+      if (FLAGS_quic_reloadable_flag_quic_enable_pcc) {
+        QUIC_FLAG_COUNT(quic_reloadable_flag_quic_enable_pcc);
+        return CreatePccSender(clock, rtt_stats, unacked_packets, random, stats,
+                               initial_congestion_window,
+                               max_congestion_window);
+      }
+    // Fall back to CUBIC if PCC is disabled.
     // FALLTHROUGH_INTENDED
     case kCubic:
       return new TcpCubicSenderPackets(