Add live mode detection in WebM MediaSource parser.

media/base/demuxer.h

Index: media/base/demuxer.h
diff --git a/media/base/demuxer.h b/media/base/demuxer.h
index 581bc0075f6f5023da5970308a6b99614a718861..5e72a18f445d0ac2a96943df21d05aa7e9fe411d 100644
--- a/media/base/demuxer.h
+++ b/media/base/demuxer.h
@@ -92,6 +92,10 @@ class MEDIA_EXPORT Demuxer {
   // a null Time is returned.
   virtual base::Time GetTimelineOffset() const = 0;
 
+  // True when the stream is a live stream. Decoders may use this flag e.g. to
+  // minimize decoding delay for live streams.
+  virtual bool IsLiveMode() const = 0;
+
  private:
   DISALLOW_COPY_AND_ASSIGN(Demuxer);
 };