Add stats totalSamplesReceived and concealedSamples

Adds two new stats to RTCMediaStreamTrackStats:
* totalSamplesReceived is the total number of samples received on
      the audio channel and includes real and synthetic samples.
* concealedSamples is the total number of synthetic samples
      received on the audio channel used to conceal packet loss.

Bug: webrtc:8076
Change-Id: I36e9828525ec341490cf3310a972b56a8b443667
Reviewed-on: https://chromium-review.googlesource.com/615902
Commit-Queue: Steve Anton <steveanton@webrtc.org>
Reviewed-by: Tommi <tommi@webrtc.org>
Reviewed-by: Taylor Brandstetter <deadbeef@webrtc.org>
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Henrik Lundin <henrik.lundin@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#19506}

webrtc/modules/audio_coding/neteq/neteq_impl.h

@@ -185,6 +185,8 @@ class NetEqImpl : public webrtc::NetEq {
   // and a new report period is started with the call.
   void GetRtcpStatistics(RtcpStatistics* stats) override;
 
+  NetEqLifetimeStatistics GetLifetimeStatistics() const override;
+
   // Same as RtcpStatistics(), but does not reset anything.
   void GetRtcpStatisticsNoReset(RtcpStatistics* stats) override;