Fix memory leak in playback time accumulation

Bug: 201941775
Test: boot, simple playback
Change-Id: If50e4cd192c9c2c5fd43301ef5535a352f236fe9
diff --git a/media/libstagefright/include/media/stagefright/MediaCodec.h b/media/libstagefright/include/media/stagefright/MediaCodec.h
index ce3b0d0..b9a3197 100644
--- a/media/libstagefright/include/media/stagefright/MediaCodec.h
+++ b/media/libstagefright/include/media/stagefright/MediaCodec.h
@@ -502,7 +502,7 @@
 
     std::shared_ptr<BufferChannelBase> mBufferChannel;
 
-    PlaybackDurationAccumulator * mPlaybackDurationAccumulator;
+    std::unique_ptr<PlaybackDurationAccumulator> mPlaybackDurationAccumulator;
     bool mIsSurfaceToScreen;
 
     MediaCodec(