NuPlayer:seek handling on kWhatAudioTearDown

Restart from previous seek time on kWhatAudioTearDown if mRenderer
didn't supply a useful positionUs.

Bug: 22662968
Change-Id: Ic21957f676ba25fb92694f71093bed60b630390b
diff --git a/media/libmediaplayerservice/nuplayer/NuPlayer.h b/media/libmediaplayerservice/nuplayer/NuPlayer.h
index 9456d5d..c9f0bbd 100644
--- a/media/libmediaplayerservice/nuplayer/NuPlayer.h
+++ b/media/libmediaplayerservice/nuplayer/NuPlayer.h
@@ -154,6 +154,8 @@
     int32_t mVideoDecoderGeneration;
     int32_t mRendererGeneration;
 
+    int64_t mPreviousSeekTimeUs;
+
     List<sp<Action> > mDeferredActions;
 
     bool mAudioEOS;