Sync audio/video/text track-related interfaces with the specs

Source/core/html/track/TextTrack.idl

 /*
  * Copyright (C) 2011 Google Inc.  All rights reserved.
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+// https://html.spec.whatwg.org/#texttrack
+
 enum TextTrackMode { "disabled",  "hidden",  "showing" };
 enum TextTrackKind { "subtitles",  "captions",  "descriptions",  "chapters",  "metadata" };
 
 [
     SetWrapperReferenceFrom=owner,
     TypeChecking=Interface,
 ] interface TextTrack : EventTarget {
     readonly attribute TextTrackKind kind;
     readonly attribute DOMString label;
     readonly attribute DOMString language;
 
     readonly attribute DOMString id;
+    // readonly attribute DOMString inBandMetadataTrackDispatchType;
 
-             attribute TextTrackMode mode;
+    attribute TextTrackMode mode;
 
-    readonly attribute TextTrackCueList cues;
-    readonly attribute TextTrackCueList activeCues;
+    readonly attribute TextTrackCueList? cues;
+    readonly attribute TextTrackCueList? activeCues;
 
     void addCue(TextTrackCue cue);
     [RaisesException] void removeCue(TextTrackCue cue);
 
-             attribute EventHandler oncuechange;
+    attribute EventHandler oncuechange;
 
+    // TODO(philipj): These WebVTT extensions have been removed from the spec:
+    // https://www.w3.org/Bugs/Public/show_bug.cgi?id=24380
     [RuntimeEnabled=WebVTTRegions] readonly attribute VTTRegionList regions;
     [RuntimeEnabled=WebVTTRegions] void addRegion(VTTRegion region);
     [RaisesException, RuntimeEnabled=WebVTTRegions] void removeRegion(VTTRegion region);
 };