Add UMA histogram for Echo likelihood.

webrtc/modules/audio_processing/residual_echo_detector.cc

Index: webrtc/modules/audio_processing/residual_echo_detector.cc
diff --git a/webrtc/modules/audio_processing/residual_echo_detector.cc b/webrtc/modules/audio_processing/residual_echo_detector.cc
index ff59dc2f5b0c1cd537aa76670b2b12b121854b5f..61cfce96a95d97e1d0007b759829d1d38de85968 100644
--- a/webrtc/modules/audio_processing/residual_echo_detector.cc
+++ b/webrtc/modules/audio_processing/residual_echo_detector.cc
@@ -14,6 +14,7 @@
 #include <numeric>
 
 #include "webrtc/modules/audio_processing/audio_buffer.h"
+#include "webrtc/system_wrappers/include/metrics.h"
 
 namespace {
 
@@ -24,6 +25,8 @@ float Power(rtc::ArrayView<const float> input) {
 constexpr size_t kLookbackFrames = 650;
 // TODO(ivoc): Verify the size of this buffer.
 constexpr size_t kRenderBufferSize = 30;
+// Number of bins in the echo likelihood histogram.
+constexpr size_t kNumberOfHistogramBins = 100;
 
 }  // namespace
 
@@ -99,6 +102,9 @@ void ResidualEchoDetector::AnalyzeCaptureAudio(
     echo_likelihood_ = std::max(
         echo_likelihood_, covariances_[delay].normalized_cross_correlation());
   }
+  int echo_percentage = static_cast<int>(echo_likelihood_ * 100);
+  RTC_HISTOGRAM_COUNTS("WebRTC.Audio.ResidualEchoDetector.EchoLikelihood",
+                       echo_percentage, 0, 100, kNumberOfHistogramBins);

[hlundin-webrtc, 2016/11/09 20:01:26]

I'm not convinced that kNumberOfHistogramBins grants improved readability.
Consider "100 /* number of bins */".

[ivoc, 2016/11/10 15:13:47]

Done.

 
   // Update the next insertion index.
   ++next_insertion_index_;