GpuVideoDecoder not to use DemuxerStream after it's stopped.

media/base/video_decoder.h

Index: media/base/video_decoder.h
diff --git a/media/base/video_decoder.h b/media/base/video_decoder.h
index 904a6fd97823e25b691df209c8c1675da92da9cd..97566da048687f6ba03d8b254e468c111f2f7091 100644
--- a/media/base/video_decoder.h
+++ b/media/base/video_decoder.h
@@ -29,7 +29,9 @@ class MEDIA_EXPORT VideoDecoder
   // Initializes a VideoDecoder with the given DemuxerStream, executing the
   // |status_cb| upon completion.
   // |statistics_cb| is used to update the global pipeline statistics.
-  // Note: No VideoDecoder calls should be made before |status_cb| is executed.
+  // Note:
+  // 1) No VideoDecoder calls should be made before |status_cb| is executed.
+  // 2) DemuxerStream should not be accessed after the VideoDecoder is stopped.
   virtual void Initialize(const scoped_refptr<DemuxerStream>& stream,
                           const PipelineStatusCB& status_cb,
                           const StatisticsCB& statistics_cb) = 0;