Cast: Let the extension control if DSCP is on or off.

media/cast/net/cast_transport_sender_impl.cc

Index: media/cast/net/cast_transport_sender_impl.cc
diff --git a/media/cast/net/cast_transport_sender_impl.cc b/media/cast/net/cast_transport_sender_impl.cc
index a6b6fa4098c4e75b00212a94f228a383fae6dfa5..ae225d39123e2d6e59d9a26d1494b7948037cd83 100644
--- a/media/cast/net/cast_transport_sender_impl.cc
+++ b/media/cast/net/cast_transport_sender_impl.cc
@@ -17,6 +17,7 @@ scoped_ptr<CastTransportSender> CastTransportSender::Create(
     net::NetLog* net_log,
     base::TickClock* clock,
     const net::IPEndPoint& remote_end_point,
+    const std::string& options,
     const CastTransportStatusCallback& status_callback,
     const BulkRawEventsCallback& raw_events_callback,
     base::TimeDelta raw_events_callback_interval,
@@ -25,6 +26,7 @@ scoped_ptr<CastTransportSender> CastTransportSender::Create(
       new CastTransportSenderImpl(net_log,
                                   clock,
                                   remote_end_point,
+                                  options,
                                   status_callback,
                                   raw_events_callback,
                                   raw_events_callback_interval,
@@ -40,6 +42,7 @@ CastTransportSenderImpl::CastTransportSenderImpl(
     net::NetLog* net_log,
     base::TickClock* clock,
     const net::IPEndPoint& remote_end_point,
+    const std::string& options,
     const CastTransportStatusCallback& status_callback,
     const BulkRawEventsCallback& raw_events_callback,
     base::TimeDelta raw_events_callback_interval,
@@ -74,9 +77,11 @@ CastTransportSenderImpl::CastTransportSenderImpl(
         raw_events_callback_interval);
   }
   if (transport_) {
-    // The default DSCP value for cast is AF41. Which gives it a higher
-    // priority over other traffic.
-    transport_->SetDscp(net::DSCP_AF41);
+    if (options.find(":DSCP:") != std::string::npos) {
+      // The default DSCP value for cast is AF41. Which gives it a higher
+      // priority over other traffic.
+      transport_->SetDscp(net::DSCP_AF41);
+    }
     transport_->StartReceiving(
         base::Bind(&CastTransportSenderImpl::OnReceivedPacket,
                    weak_factory_.GetWeakPtr()));