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

media/cast/net/cast_transport_sender.h

Index: media/cast/net/cast_transport_sender.h
diff --git a/media/cast/net/cast_transport_sender.h b/media/cast/net/cast_transport_sender.h
index b3d5c701ee697ec8f41bfa356c100d6436773c67..46031a886e9938ba579c090dc0ce7a637ba4daf9 100644
--- a/media/cast/net/cast_transport_sender.h
+++ b/media/cast/net/cast_transport_sender.h
@@ -30,6 +30,10 @@
 #include "media/cast/net/rtcp/rtcp_defines.h"
 #include "net/base/ip_endpoint.h"
 
+namespace base {
+class DictionaryValue;
+}  // namespace base
+
 namespace net {
 class NetLog;
 }  // namespace net
@@ -53,6 +57,7 @@ class CastTransportSender : public base::NonThreadSafe {
       net::NetLog* net_log,
       base::TickClock* clock,
       const net::IPEndPoint& remote_end_point,
+      scoped_ptr<base::DictionaryValue> options,
       const CastTransportStatusCallback& status_callback,
       const BulkRawEventsCallback& raw_events_callback,
       base::TimeDelta raw_events_callback_interval,