QUIC congestion option that forces ICWND to 10. Not flag protected.

net/quic/congestion_control/tcp_cubic_sender.cc

Index: net/quic/congestion_control/tcp_cubic_sender.cc
diff --git a/net/quic/congestion_control/tcp_cubic_sender.cc b/net/quic/congestion_control/tcp_cubic_sender.cc
index bd61bdb916ec3c7f2cb50beb9418e58fb829749d..18401b713b7d11f23925d14f36a161d6e6a4a275 100644
--- a/net/quic/congestion_control/tcp_cubic_sender.cc
+++ b/net/quic/congestion_control/tcp_cubic_sender.cc
@@ -8,6 +8,7 @@
 
 #include "base/metrics/histogram.h"
 #include "net/quic/congestion_control/rtt_stats.h"
+#include "net/quic/crypto/crypto_protocol.h"
 
 using std::max;
 using std::min;
@@ -58,10 +59,18 @@ TcpCubicSender::~TcpCubicSender() {
 }
 
 void TcpCubicSender::SetFromConfig(const QuicConfig& config, bool is_server) {
-  if (is_server && config.HasReceivedInitialCongestionWindow()) {
-    // Set the initial window size.
-    congestion_window_ = min(kMaxInitialWindow,
-                             config.ReceivedInitialCongestionWindow());
+  if (is_server) {
+    if (config.HasReceivedConnectionOptions() &&
+        ContainsQuicTag(config.ReceivedConnectionOptions(), kIW10)) {
+      // Initial window experiment.  Ignore the initial congestion
+      // window suggested by the client and use the default ICWND of
+      // 10 instead.
+      congestion_window_ = kInitialCongestionWindow;
+    } else if (config.HasReceivedInitialCongestionWindow()) {
+      // Set the initial window size.
+      congestion_window_ = min(kMaxInitialWindow,
+                               config.ReceivedInitialCongestionWindow());
+    }
   }
 }