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

media/cast/test/cast_benchmarks.cc

Index: media/cast/test/cast_benchmarks.cc
diff --git a/media/cast/test/cast_benchmarks.cc b/media/cast/test/cast_benchmarks.cc
index deec12ca538a56be1a05b3e0bd9b9c8fa0ac0f01..c85befd521dc7fc21573efaac864a64f80089c9b 100644
--- a/media/cast/test/cast_benchmarks.cc
+++ b/media/cast/test/cast_benchmarks.cc
@@ -302,6 +302,7 @@ class RunOneBenchmark {
             NULL,
             testing_clock_sender_,
             dummy_endpoint,
+            "",
             base::Bind(&UpdateCastTransportStatus),
             base::Bind(&IgnoreRawEvents),
             base::TimeDelta::FromSeconds(1),