Adding stats that can be used to compute output audio levels.

webrtc/api/stats/rtcstats_objects.h

Index: webrtc/api/stats/rtcstats_objects.h
diff --git a/webrtc/api/stats/rtcstats_objects.h b/webrtc/api/stats/rtcstats_objects.h
index 49135f89a1a1250563023fe17063fc0762dcd148..d73c3b8327d40793dc734750776ec9d737a08e75 100644
--- a/webrtc/api/stats/rtcstats_objects.h
+++ b/webrtc/api/stats/rtcstats_objects.h
@@ -272,6 +272,8 @@ class RTCMediaStreamTrackStats final : public RTCStats {
   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;
 };