AudioFlinger: Add latency measurements from timestamp

Replaces main and aux buf from track dump.

Bug: 80272001
Test: adb shell dumpsys media.audio_flinger
Change-Id: I5d6565410e652ec7fc6701b171d299dea9f7bc3e
diff --git a/services/audioflinger/FastMixerDumpState.h b/services/audioflinger/FastMixerDumpState.h
index 8ef31d1..aed6bc5 100644
--- a/services/audioflinger/FastMixerDumpState.h
+++ b/services/audioflinger/FastMixerDumpState.h
@@ -66,6 +66,7 @@
 
     void dump(int fd) const;    // should only be called on a stable copy, not the original
 
+    double   mLatencyMs = 0.;   // measured latency, default of 0 if no valid timestamp read.
     uint32_t mWriteSequence;    // incremented before and after each write()
     uint32_t mFramesWritten;    // total number of frames written successfully
     uint32_t mNumTracks;        // total number of active fast tracks