Document calls to the "rules for updating the text track rendering"

Source/core/html/track/TextTrackContainer.cpp

Index: Source/core/html/track/TextTrackContainer.cpp
diff --git a/Source/core/html/track/TextTrackContainer.cpp b/Source/core/html/track/TextTrackContainer.cpp
index 22f276c85fd53416eabf442a13b3703756f06de6..099502d33485bbcaee883c728c4a2bf6c5287e5e 100644
--- a/Source/core/html/track/TextTrackContainer.cpp
+++ b/Source/core/html/track/TextTrackContainer.cpp
@@ -61,6 +61,8 @@ void TextTrackContainer::updateDisplay(HTMLMediaElement& mediaElement)
         return;
     }
 
+    // http://dev.w3.org/html5/webvtt/#dfn-rules-for-updating-the-display-of-webvtt-text-tracks
+
     // 1. If the media element is an audio element, or is another playback
     // mechanism with no rendering area, abort these steps. There is nothing to
     // render.