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

media/filters/chunk_demuxer.cc

Index: media/filters/chunk_demuxer.cc
diff --git a/media/filters/chunk_demuxer.cc b/media/filters/chunk_demuxer.cc
index fa14f1333f15ba3d0d30a68a8506e7e15797e9d4..374d618c5a0c034a9b0301566f6bb7c77d020ccd 100644
--- a/media/filters/chunk_demuxer.cc
+++ b/media/filters/chunk_demuxer.cc
@@ -160,12 +160,11 @@
   return stream_->GetBufferedSize();
 }
 
-void ChunkDemuxerStream::OnStartOfCodedFrameGroup(
-    DecodeTimestamp start_timestamp) {
-  DVLOG(2) << "ChunkDemuxerStream::OnStartOfCodedFrameGroup("
+void ChunkDemuxerStream::OnNewMediaSegment(DecodeTimestamp start_timestamp) {
+  DVLOG(2) << "ChunkDemuxerStream::OnNewMediaSegment("
            << start_timestamp.InSecondsF() << ")";
   base::AutoLock auto_lock(lock_);
-  stream_->OnStartOfCodedFrameGroup(start_timestamp);
+  stream_->OnNewMediaSegment(start_timestamp);
 }
 
 bool ChunkDemuxerStream::UpdateAudioConfig(