AudioTrack: When paused, return cached playback position

An offload output can be re-used between two audio tracks having
the same configuration. A timestamp query for a paused track
while the other is running would return an incorrect time.
To fix this, cache the playback position on a pause() and return
this time when requested until the track is resumed.

Bug: 12826612.
Change-Id: I324112ea9827e52fff53ef44cd8513c8d85a0bc4
diff --git a/include/media/AudioTrack.h b/include/media/AudioTrack.h
index 7e9d557..7d23d02 100644
--- a/include/media/AudioTrack.h
+++ b/include/media/AudioTrack.h
@@ -746,6 +746,7 @@
 
     bool                    mInUnderrun;            // whether track is currently in underrun state
     String8                 mName;                  // server's name for this IAudioTrack
+    uint32_t                mPausedPosition;
 
 private:
     class DeathNotifier : public IBinder::DeathRecipient {