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/api/stats/rtcstats_objects.h b/webrtc/api/stats/rtcstats_objects.h
index 49135f8..d73c3b8 100644
--- a/webrtc/api/stats/rtcstats_objects.h
+++ b/webrtc/api/stats/rtcstats_objects.h
@@ -272,6 +272,8 @@
   RTCStatsMember<uint32_t> full_frames_lost;
   // Audio-only members
   RTCStatsMember<double> audio_level;
+  RTCStatsMember<double> total_audio_energy;
+  RTCStatsMember<double> total_samples_duration;
   RTCStatsMember<double> echo_return_loss;
   RTCStatsMember<double> echo_return_loss_enhancement;
 };