Fix Media.Video.KeyFrameDistance metric calculation

media/filters/decoder_stream_traits.cc

Index: media/filters/decoder_stream_traits.cc
diff --git a/media/filters/decoder_stream_traits.cc b/media/filters/decoder_stream_traits.cc
index 645a1de417b6dd9b817e5f27368b797dc408feb6..fcbc19e4baa8e7f680afb3b22f3caa0d6842a03c 100644
--- a/media/filters/decoder_stream_traits.cc
+++ b/media/filters/decoder_stream_traits.cc
@@ -144,6 +144,7 @@ void DecoderStreamTraits<DemuxerStream::VIDEO>::OnDecode(
   UMA_HISTOGRAM_MEDIUM_TIMES(
       "Media.Video.KeyFrameDistance",
       current_frame_timestamp - last_keyframe_timestamp_);
+  last_keyframe_timestamp_ = current_frame_timestamp;
 }
 
 }  // namespace media