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}
diff --git a/webrtc/pc/rtcstatscollector_unittest.cc b/webrtc/pc/rtcstatscollector_unittest.cc
index 4f3b35f..cc258ed 100644
--- a/webrtc/pc/rtcstatscollector_unittest.cc
+++ b/webrtc/pc/rtcstatscollector_unittest.cc
@@ -1554,7 +1554,9 @@
   voice_receiver_info.local_stats[0].ssrc = 3;
   voice_receiver_info.audio_level = 16383;
   voice_receiver_info.total_output_energy = 0.125;
+  voice_receiver_info.total_samples_received = 4567;
   voice_receiver_info.total_output_duration = 0.25;
+  voice_receiver_info.concealed_samples = 123;
 
   test_->CreateMockRtpSendersReceiversAndChannels(
       { std::make_pair(local_audio_track.get(), voice_sender_info_ssrc1),
@@ -1628,7 +1630,9 @@
   expected_remote_audio_track.detached = false;
   expected_remote_audio_track.audio_level = 16383.0 / 32767.0;
   expected_remote_audio_track.total_audio_energy = 0.125;
+  expected_remote_audio_track.total_samples_received = 4567;
   expected_remote_audio_track.total_samples_duration = 0.25;
+  expected_remote_audio_track.concealed_samples = 123;
   ASSERT_TRUE(report->Get(expected_remote_audio_track.id()));
   EXPECT_EQ(expected_remote_audio_track,
             report->Get(expected_remote_audio_track.id())->cast_to<