Introducing DemuxerHost::OnMetadata.

media/base/demuxer.h

Index: media/base/demuxer.h
diff --git a/media/base/demuxer.h b/media/base/demuxer.h
index 0d2219853240e3e07f1d0c0d3089e84bead79624..0bc990253df8fbe1a957c51655b2be2d3279d6e8 100644
--- a/media/base/demuxer.h
+++ b/media/base/demuxer.h
@@ -18,6 +18,7 @@
 #include "media/base/eme_constants.h"
 #include "media/base/media_export.h"
 #include "media/base/media_track.h"
+#include "media/base/pipeline_metadata.h"
 #include "media/base/pipeline_status.h"
 #include "media/base/ranges.h"
 
@@ -28,6 +29,9 @@ class MediaTracks;
 
 class MEDIA_EXPORT DemuxerHost {
  public:
+  // Executed when the content metadata is known.
+  virtual void OnMetadata(PipelineMetadata metadata) = 0;
+
   // Notify the host that buffered time ranges have changed. Note that buffered
   // time ranges can grow (when new media data is appended), but they can also
   // shrink (when buffering reaches limit capacity and some buffered data