Add logging of written frame counts

Bug: 31591209
Change-Id: Ife5917aa65b02c3b0791dfe1975c70ccf58f9a75
(cherry picked from commit 2c45393d842a5d2968ef78fa7a08667efdf15f2a)
diff --git a/services/audioflinger/FastMixerDumpState.h b/services/audioflinger/FastMixerDumpState.h
index ac15e7c..301c5b1 100644
--- a/services/audioflinger/FastMixerDumpState.h
+++ b/services/audioflinger/FastMixerDumpState.h
@@ -57,6 +57,7 @@
     /*virtual*/ ~FastTrackDump() { }
     FastTrackUnderruns  mUnderruns;
     size_t              mFramesReady;        // most recent value only; no long-term statistics kept
+    int64_t             mFramesWritten;      // last value from track
 };
 
 struct FastMixerDumpState : FastThreadDumpState {