Adding test for SingleNalUnit mode

modules/video_coding/codecs/test/stats.h

Index: modules/video_coding/codecs/test/stats.h
diff --git a/modules/video_coding/codecs/test/stats.h b/modules/video_coding/codecs/test/stats.h
index 8022f277c83c34886e2f11624543d42ac6b3c72f..fd6fa874b2521fd226c3078bb60bc1fc477fe225 100644
--- a/modules/video_coding/codecs/test/stats.h
+++ b/modules/video_coding/codecs/test/stats.h
@@ -32,6 +32,9 @@ struct FrameStatistic {
   size_t encoded_frame_size_bytes = 0;
   webrtc::FrameType frame_type = kVideoFrameDelta;
 
+  // H264 specific.
+  rtc::Optional<size_t> max_nalu_length;
+
   // Decoding.
   int64_t decode_start_ns = 0;
   int decode_return_code = 0;