Run Demuxer::GetMemoryUsage() on media thread

media/blink/webmediaplayer_impl.h

Index: media/blink/webmediaplayer_impl.h
diff --git a/media/blink/webmediaplayer_impl.h b/media/blink/webmediaplayer_impl.h
index c3ad6a630a6ac18c70b46df36201763627d8830f..5d77056028e810d1f65158b3795894a67eb5ed81 100644
--- a/media/blink/webmediaplayer_impl.h
+++ b/media/blink/webmediaplayer_impl.h
@@ -241,7 +241,10 @@ class MEDIA_BLINK_EXPORT WebMediaPlayerImpl
 
   // Called at low frequency to tell external observers how much memory we're
   // using for video playback.  Called by |memory_usage_reporting_timer_|.
-  void ReportMemoryUsage();
+  // Memory usage reporting is done in two steps, because |demuxer_| must be
+  // accessed on the media thread.
+  void StartMemoryUsageReport();
+  void FinishMemoryUsageReport(int64_t demuxer_memory_usage);
 
   blink::WebLocalFrame* frame_;