Reland: MSE: Relax the 'media segment must begin with keyframe' requirement

media/formats/mp2t/mp2t_stream_parser.cc

Index: media/formats/mp2t/mp2t_stream_parser.cc
diff --git a/media/formats/mp2t/mp2t_stream_parser.cc b/media/formats/mp2t/mp2t_stream_parser.cc
index 3bc8d25c6bfccd73bb48432fe5037e0ffb8d3b74..12c8a82d4b6230923934a508543f4ed04fe14ac3 100644
--- a/media/formats/mp2t/mp2t_stream_parser.cc
+++ b/media/formats/mp2t/mp2t_stream_parser.cc
@@ -180,6 +180,7 @@ void Mp2tStreamParser::Init(
   DCHECK(!config_cb.is_null());
   DCHECK(!new_buffers_cb.is_null());
   DCHECK(!encrypted_media_init_data_cb.is_null());
+  DCHECK(!new_segment_cb.is_null());
   DCHECK(!end_of_segment_cb.is_null());
 
   init_cb_ = init_cb;