Ensure media's buffered ranges always have a range that includes currentTime.

media/base/demuxer_stream.h

Index: media/base/demuxer_stream.h
diff --git a/media/base/demuxer_stream.h b/media/base/demuxer_stream.h
index 4168d04ee3165260731e374a7e49b906e0400f28..1266a712687c3b8030db72ea28acb8c4dc1c3030 100644
--- a/media/base/demuxer_stream.h
+++ b/media/base/demuxer_stream.h
@@ -8,6 +8,7 @@
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "media/base/media_export.h"
+#include "media/base/ranges.h"
 
 namespace media {
 
@@ -41,6 +42,9 @@ class MEDIA_EXPORT DemuxerStream
   // if type() != VIDEO.
   virtual const VideoDecoderConfig& video_decoder_config() = 0;
 
+  // Returns time ranges known to have been seen by this stream.
+  virtual Ranges<base::TimeDelta> GetBufferedRanges() = 0;
+
   // Returns the type of stream.
   virtual Type type() = 0;