Screen content simulcast layers should not be downscaled.

webrtc/media/engine/simulcast.cc

Index: webrtc/media/engine/simulcast.cc
diff --git a/webrtc/media/engine/simulcast.cc b/webrtc/media/engine/simulcast.cc
index 62587f682d2683302483b1d1719323d6fa891d21..8378ca342d3504278b9ab3fdfe6f12afc581f787 100644
--- a/webrtc/media/engine/simulcast.cc
+++ b/webrtc/media/engine/simulcast.cc
@@ -230,8 +230,10 @@ std::vector<webrtc::VideoStream> GetSimulcastConfig(size_t max_streams,
       streams[s].max_framerate = max_framerate;
     }
 
-    width /= 2;
-    height /= 2;
+    if (!is_screencast) {
+      width /= 2;
+      height /= 2;
+    }
     if (s == 0)
       break;
   }