Log BufferedResourceLoader events to MediaLog.

media/base/media_log_event.h

Index: media/base/media_log_event.h
diff --git a/media/base/media_log_event.h b/media/base/media_log_event.h
index dd1735e27c920bab65e3785689cbe7c5dfb75ec6..0c8e3da0408b7fb8fea74dd3190cf8636fb15f83 100644
--- a/media/base/media_log_event.h
+++ b/media/base/media_log_event.h
@@ -26,6 +26,12 @@ struct MediaLogEvent {
     // params: none.
     PLAY,
     PAUSE,
+
+    // The extents of the sliding buffer have changed.
+    // params: "buffer_start": <first buffered byte>.
+    //         "buffer_current": <current offset>.
+    //         "buffer_end": <last buffered byte>.
+    BUFFERED_EXTENTS_CHANGED,
   };
 
   int32 id;