Don't use control block frame count after create

This is part of a series to clean up the control block.

Change-Id: I7f4cb05aef63053f8e2ab05b286d302260ef4758
diff --git a/services/audioflinger/AudioFlinger.h b/services/audioflinger/AudioFlinger.h
index 830dfe9..75bfcfe 100644
--- a/services/audioflinger/AudioFlinger.h
+++ b/services/audioflinger/AudioFlinger.h
@@ -478,6 +478,8 @@
             const size_t        mFrameSize; // AudioFlinger's view of frame size in shared memory,
                                             // where for AudioTrack (but not AudioRecord),
                                             // 8-bit PCM samples are stored as 16-bit
+            const size_t        mFrameCount;// size of track buffer given at createTrack() or
+                                            // openRecord(), and then adjusted as needed
             bool                mStepServerFailed;
             const int           mSessionId;
             Vector < sp<SyncEvent> >mSyncEvents;