Add UMA stats to bad call detection.

webrtc/video/quality_threshold.cc

Index: webrtc/video/quality_threshold.cc
diff --git a/webrtc/video/quality_threshold.cc b/webrtc/video/quality_threshold.cc
index 3f2d835e80b2b7e3332cc5501ec214c3ef689a5a..c1d3b101ebc7018926f9eb9189ef93a317190175 100644
--- a/webrtc/video/quality_threshold.cc
+++ b/webrtc/video/quality_threshold.cc
@@ -28,7 +28,9 @@ QualityThreshold::QualityThreshold(int low_threshold,
       next_index_(0),
       sum_(0),
       count_low_(0),
-      count_high_(0) {
+      count_high_(0),
+      num_high_states_(0),
+      num_certain_states_(0) {
   RTC_CHECK_GT(fraction, 0.5f);
   RTC_CHECK_GT(max_measurements, 1);
   RTC_CHECK_LT(low_threshold, high_threshold);
@@ -64,6 +66,12 @@ void QualityThreshold::AddMeasurement(int measurement) {
 
   if (until_full_ > 0)
     --until_full_;
+
+  if (is_high_) {
+    if (*is_high_)
+      ++num_high_states_;
+    ++num_certain_states_;
+  }
 }
 
 rtc::Optional<bool> QualityThreshold::IsHigh() const {
@@ -83,4 +91,14 @@ rtc::Optional<double> QualityThreshold::CalculateVariance() const {
   return rtc::Optional<double>(variance / (max_measurements_ - 1));
 }
 
+rtc::Optional<double> QualityThreshold::FractionHigh(
+    int min_required_samples) const {
+  RTC_DCHECK_GT(min_required_samples, 0);
+  if (num_certain_states_ < min_required_samples)
+    return rtc::Optional<double>();
+
+  return rtc::Optional<double>(static_cast<double>(num_high_states_) /
+                               num_certain_states_);
+}
+
 }  // namespace webrtc