Add new decoding statistics for muted output

This change adds a new statistic for logging how many calls to
NetEq::GetAudio resulted in a "muted output". A muted output happens
if the packet stream has been dead for some time (and the last decoded
packet was not comfort noise).

BUG=webrtc:5606
BUG=b/31256483

Review-Url: https://codereview.webrtc.org/2341293002
Cr-Commit-Position: refs/heads/master@{#14302}
diff --git a/webrtc/modules/audio_coding/acm2/acm_receiver.cc b/webrtc/modules/audio_coding/acm2/acm_receiver.cc
index 9a882aa..417a346 100644
--- a/webrtc/modules/audio_coding/acm2/acm_receiver.cc
+++ b/webrtc/modules/audio_coding/acm2/acm_receiver.cc
@@ -135,6 +135,7 @@
 int AcmReceiver::GetAudio(int desired_freq_hz,
                           AudioFrame* audio_frame,
                           bool* muted) {
+  RTC_DCHECK(muted);
   // Accessing members, take the lock.
   rtc::CritScope lock(&crit_sect_);
 
@@ -191,7 +192,7 @@
          sizeof(int16_t) * audio_frame->samples_per_channel_ *
              audio_frame->num_channels_);
 
-  call_stats_.DecodedByNetEq(audio_frame->speech_type_);
+  call_stats_.DecodedByNetEq(audio_frame->speech_type_, *muted);
   return 0;
 }