NuPlayer: Add audio callback mode for PCM audio.

Disabled for now. Enabled by property media.stagefright.audio.cbk 1

Bug: 21198655
Change-Id: I8f117b089fe019009f1615908d33720a93e1b21e
diff --git a/media/libmediaplayerservice/nuplayer/NuPlayerRenderer.h b/media/libmediaplayerservice/nuplayer/NuPlayerRenderer.h
index fbdf5bf..c2fea40 100644
--- a/media/libmediaplayerservice/nuplayer/NuPlayerRenderer.h
+++ b/media/libmediaplayerservice/nuplayer/NuPlayerRenderer.h
@@ -194,6 +194,7 @@
 
     int32_t mTotalBuffersQueued;
     int32_t mLastAudioBufferDrained;
+    bool mUseAudioCallback;
 
     sp<AWakeLock> mWakeLock;