Add support for cancellation of demuxer reads.

media/base/demuxer.h

Index: media/base/demuxer.h
diff --git a/media/base/demuxer.h b/media/base/demuxer.h
index 0d2219853240e3e07f1d0c0d3089e84bead79624..ae07e60b33ce698965f0d6689d75879c70654088 100644
--- a/media/base/demuxer.h
+++ b/media/base/demuxer.h
@@ -88,6 +88,10 @@ class MEDIA_EXPORT Demuxer : public DemuxerStreamProvider {
                           const PipelineStatusCB& status_cb,
                           bool enable_text_tracks) = 0;
 
+  // Aborts any pending read operations that the demuxer is involved with; any
+  // read aborted will be aborted with a status of kAborted.
+  virtual void AbortPendingReads() = 0;
+
   // Indicates that a new Seek() call is on its way. Implementations may abort
   // pending reads and future Read() calls may return kAborted until Seek() is
   // executed. |seek_time| is the presentation timestamp of the new Seek() call.