MediaMetrics: Add AudioFlinger logging

Test: atest mediametrics_tests
Test: mediametrics dumpsys
Bug: 138583596
Change-Id: I2086c5a780744d409052fde4c5ebc1dc92d95ea8
diff --git a/services/audioflinger/Threads.h b/services/audioflinger/Threads.h
index f1adc23..b0eb75d 100644
--- a/services/audioflinger/Threads.h
+++ b/services/audioflinger/Threads.h
@@ -523,6 +523,7 @@
                 Condition               mWaitWorkCV;
 
                 const sp<AudioFlinger>  mAudioFlinger;
+                const std::string       mMetricsId;
 
                 // updated by PlaybackThread::readOutputParameters_l() or
                 // RecordThread::readInputParameters_l()