Add experimental simulcast screen content mode

webrtc/media/engine/simulcast.h

Index: webrtc/media/engine/simulcast.h
diff --git a/webrtc/media/engine/simulcast.h b/webrtc/media/engine/simulcast.h
index 20be4c487e443f5b20bc0e051d2931817590ca84..a738d630fd80d66201ed9b0e1da6743dcf04267d 100644
--- a/webrtc/media/engine/simulcast.h
+++ b/webrtc/media/engine/simulcast.h
@@ -19,6 +19,7 @@
 namespace cricket {
 struct StreamParams;
 
+// TODO(sprang): Remove this, as we're moving away from temporal layer mode.
 // Config for use with screen cast when temporal layers are enabled.
 struct ScreenshareLayerConfig {
  public:
@@ -50,7 +51,10 @@ std::vector<webrtc::VideoStream> GetSimulcastConfig(size_t max_streams,
                                                     int height,
                                                     int max_bitrate_bps,
                                                     int max_qp,
-                                                    int max_framerate);
+                                                    int max_framerate,
+                                                    bool is_screencast);
+
+bool UseSimulcastScreenshare();
 
 }  // namespace cricket