Add histogram stats for number of cpu/quality adapt changes per minute for sent video streams:

webrtc/video/vie_encoder.cc

Index: webrtc/video/vie_encoder.cc
diff --git a/webrtc/video/vie_encoder.cc b/webrtc/video/vie_encoder.cc
index aa5e593ed853ee47d05e712469f41691582a9742..ecf3a547ee74af7fbb7fad7ad753837c3e4b026f 100644
--- a/webrtc/video/vie_encoder.cc
+++ b/webrtc/video/vie_encoder.cc
@@ -541,7 +541,7 @@ void ViEEncoder::ConfigureQualityScaler() {
 
   const std::vector<int>& scale_counters = GetScaleCounters();
   stats_proxy_->SetCpuScalingStats(
-      degradation_preference_allows_scaling ? scale_counters[kCpu] > 0 : false);
+      degradation_preference_allows_scaling ? scale_counters[kCpu] : -1);
   stats_proxy_->SetQualityScalingStats(
       quality_scaling_allowed ? scale_counters[kQuality] : -1);