AudioFlinger: Add record frames read to dumpsys

Allows comparison to playback frames written for patches.

Test: audioflinger dumpsys
Change-Id: I2ef0ccbc36819d48b05756115de70f5a24a2c2cd
diff --git a/services/audioflinger/Threads.h b/services/audioflinger/Threads.h
index 2ab0bee..705efbc 100644
--- a/services/audioflinger/Threads.h
+++ b/services/audioflinger/Threads.h
@@ -1601,6 +1601,8 @@
             bool                                mFastTrackAvail;    // true if fast track available
             // common state to all record threads
             std::atomic_bool                    mBtNrecSuspended;
+
+            int64_t                             mFramesRead = 0;    // continuous running counter.
 };
 
 class MmapThread : public ThreadBase