[Video] Collect average keyframe distance for video

media/filters/decoder_stream_traits.h

Index: media/filters/decoder_stream_traits.h
diff --git a/media/filters/decoder_stream_traits.h b/media/filters/decoder_stream_traits.h
index 63951c1325fc044811fab64ec881edd269a784e4..416b5740070890dc9dcfd9eb56827c775f2dcc1b 100644
--- a/media/filters/decoder_stream_traits.h
+++ b/media/filters/decoder_stream_traits.h
@@ -5,8 +5,10 @@
 #ifndef MEDIA_FILTERS_DECODER_STREAM_TRAITS_H_
 #define MEDIA_FILTERS_DECODER_STREAM_TRAITS_H_
 
+#include "base/time/time.h"
 #include "media/base/cdm_context.h"
 #include "media/base/demuxer_stream.h"
+#include "media/base/moving_average.h"
 #include "media/base/pipeline_status.h"
 #include "media/base/video_decoder_config.h"
 #include "media/filters/audio_timestamp_validator.h"
@@ -75,16 +77,23 @@ class MEDIA_EXPORT DecoderStreamTraits<DemuxerStream::VIDEO> {
                                int bytes_decoded);
   static scoped_refptr<OutputType> CreateEOSOutput();
 
-  explicit DecoderStreamTraits(const scoped_refptr<MediaLog>& media_log) {}
+  explicit DecoderStreamTraits(const scoped_refptr<MediaLog>& media_log);
 
   void InitializeDecoder(DecoderType* decoder,
                          DemuxerStream* stream,
                          CdmContext* cdm_context,
                          const InitCB& init_cb,
                          const OutputCB& output_cb);
-  void OnDecode(const scoped_refptr<DecoderBuffer>& buffer) {}
+  void OnDecode(const scoped_refptr<DecoderBuffer>& buffer);
   void OnDecodeDone(const scoped_refptr<OutputType>& buffer) {}
-  void OnStreamReset(DemuxerStream* stream) {}
+  void OnStreamReset(DemuxerStream* stream);
+
+ private:
+  void ResetMetrics();
+
+  MovingAverage keyframe_distance_average_;
+  base::TimeDelta last_keyframe_timestamp_;
+  base::TimeDelta max_average_;
 };
 
 }  // namespace media