Introduce DecodeTimestamp class to make it easier to distiguish presentation and decode timestamps.

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 c80ee9ea2d1e1ec8a9694bd9fc2e10a0c6920435..ff4337d157bcac9c55d0b8735bf163fd861513b1 100644
--- a/media/filters/chunk_demuxer.cc
+++ b/media/filters/chunk_demuxer.cc
@@ -854,7 +854,7 @@ TimeDelta ChunkDemuxerStream::GetBufferedDuration() const {
   return stream_->GetBufferedDuration();
 }
 
-void ChunkDemuxerStream::OnNewMediaSegment(TimeDelta start_timestamp) {
+void ChunkDemuxerStream::OnNewMediaSegment(DecodeTimestamp start_timestamp) {
   DVLOG(2) << "ChunkDemuxerStream::OnNewMediaSegment("
            << start_timestamp.InSecondsF() << ")";
   base::AutoLock auto_lock(lock_);