Add default downscale threshold to QualityScaler.

webrtc/modules/video_coding/utility/include/quality_scaler.h

Index: webrtc/modules/video_coding/utility/include/quality_scaler.h
diff --git a/webrtc/modules/video_coding/utility/include/quality_scaler.h b/webrtc/modules/video_coding/utility/include/quality_scaler.h
index 325343544aa10f8a97ae5893268772ab9eb7c394..1d6c917ec4e8f671bb6b88b9f0eaf2ab4a6d1d35 100644
--- a/webrtc/modules/video_coding/utility/include/quality_scaler.h
+++ b/webrtc/modules/video_coding/utility/include/quality_scaler.h
@@ -15,9 +15,10 @@
 #include "webrtc/modules/video_coding/utility/include/moving_average.h"
 
 namespace webrtc {
-const int kDefaultLowQpDenominator = 3;
 class QualityScaler {
  public:
+  static const int kDefaultLowQpDenominator;
+  static const int kDefaultMinDownscaleDimension;
   struct Resolution {
     int width;
     int height;