Introduce struct MediaConfig, with construction-time settings.

talk/app/webrtc/peerconnection.cc

Index: talk/app/webrtc/peerconnection.cc
diff --git a/talk/app/webrtc/peerconnection.cc b/talk/app/webrtc/peerconnection.cc
index c375e2921565acdf7ad842905f067ec5bce20115..ca7b4acf9158ef29325f4cc9cb693fbab4c718bc 100644
--- a/talk/app/webrtc/peerconnection.cc
+++ b/talk/app/webrtc/peerconnection.cc
@@ -633,7 +633,22 @@ bool PeerConnection::Initialize(
   // No step delay is used while allocating ports.
   port_allocator_->set_step_delay(cricket::kMinimumStepDelay);
 
-  media_controller_.reset(factory_->CreateMediaController());
+  // We rely on default values when constraints aren't found.
+  MediaConfig media_config;
+
+  media_config.disable_prerenderer_smoothing =
+    configuration.disable_prerenderer_smoothing;
+
+  // Find DSCP constraint.
+  FindConstraint(constraints,
+                 MediaConstraintsInterface::kEnableDscp,
+                 &media_config.enable_dscp, NULL);
+  // Find constraints for cpu overuse detection.
+  FindConstraint(constraints,
+                 MediaConstraintsInterface::kCpuOveruseDetection,
+                 &media_config.cpu_overuse_detection, NULL);
+
+  media_controller_.reset(factory_->CreateMediaController(media_config));
 
   remote_stream_factory_.reset(new RemoteMediaStreamFactory(
       factory_->signaling_thread(), media_controller_->channel_manager()));