Add histogram for percentage of sent frames that are limited in resolution due to quality.

webrtc/video/send_statistics_proxy.h

Index: webrtc/video/send_statistics_proxy.h
diff --git a/webrtc/video/send_statistics_proxy.h b/webrtc/video/send_statistics_proxy.h
index 6366e5d945a56e14dcd72b2e6ce83e9e8da74753..cd2327e2aa85213ee1d2b06f04f469938112db03 100644
--- a/webrtc/video/send_statistics_proxy.h
+++ b/webrtc/video/send_statistics_proxy.h
@@ -134,6 +134,8 @@ class SendStatisticsProxy : public CpuOveruseMetricsObserver,
   SampleCounter sent_height_counter_ GUARDED_BY(crit_);
   SampleCounter encode_time_counter_ GUARDED_BY(crit_);
   BoolSampleCounter key_frame_counter_ GUARDED_BY(crit_);
+  BoolSampleCounter quality_limited_frame_counter_ GUARDED_BY(crit_);
+  SampleCounter quality_downscales_counter_ GUARDED_BY(crit_);
 };
 
 }  // namespace webrtc