[Fuchsia] Fix FuchsiaAudioRenderer to report decoder stats.

Previously FuchsiaAudioRenderer wasn't reporting any statistics to the
pipeline. As the result the pipeline was always reporting 0 for
audio_decoded_bytes. Fixed it to report this parameter after every
packet it sent to the AudioConsumer. Note that decoding itself is
handled by the AudioConsumer implementation, so the data may be decoded
a bit later than it's reported.

Bug: 1067068
Change-Id: Iecbce0d757b6c753360073faf5a073b71b33e1f6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2148379
Auto-Submit: Sergey Ulanov <sergeyu@chromium.org>
Commit-Queue: Kevin Marshall <kmarshall@chromium.org>
Reviewed-by: Kevin Marshall <kmarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#760561}

media/fuchsia/audio/fuchsia_audio_renderer.cc

@@ -254,7 +254,6 @@ void FuchsiaAudioRenderer::StartTicking() {
     SetPlaybackState(PlaybackState::kStarting);
   }
 
-
   audio_consumer_->Start(flags, fuchsia::media::NO_TIMESTAMP,
                          media_pos.ToZxDuration());
 }
@@ -528,6 +527,13 @@ void FuchsiaAudioRenderer::OnDemuxerStreamReadDone(
     OnStreamSendDone(buffer_index);
   });
 
+  // AudioConsumer doesn't report exact time when the data is decoded, but it's
+  // safe to report it as decoded right away since the packet is expected to be
+  // decoded soon after AudioConsumer receives it.
+  PipelineStatistics stats;
+  stats.audio_bytes_decoded = buffer->data_size();
+  client_->OnStatisticsUpdate(stats);
+
   last_packet_timestamp_ = buffer->timestamp();
 
   ScheduleReadDemuxerStream();