Adding stats that can be used to compute output audio levels as described here https://w3c.github.io/webrtc-stats/#dom-rtcmediastreamtrackstats-totalaudioenergy.

BUG=webrtc:7982

Review-Url: https://codereview.webrtc.org/2964593002
Cr-Commit-Position: refs/heads/master@{#19027}
diff --git a/webrtc/audio/audio_receive_stream.cc b/webrtc/audio/audio_receive_stream.cc
index 6dedca5..d9829c7 100644
--- a/webrtc/audio/audio_receive_stream.cc
+++ b/webrtc/audio/audio_receive_stream.cc
@@ -187,6 +187,8 @@
   }
   stats.delay_estimate_ms = channel_proxy_->GetDelayEstimate();
   stats.audio_level = channel_proxy_->GetSpeechOutputLevelFullRange();
+  stats.total_output_energy = channel_proxy_->GetTotalOutputEnergy();
+  stats.total_output_duration = channel_proxy_->GetTotalOutputDuration();
 
   // Get jitter buffer and total delay (alg + jitter + playout) stats.
   auto ns = channel_proxy_->GetNetworkStatistics();