MSE: Implement TrackDefault object

Source/core/html/track/TextTrack.cpp

 /*
  * Copyright (C) 2011 Google Inc.  All rights reserved.
  * Copyright (C) 2011, 2012, 2013 Apple Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 123 matching lines @@
     if (value == descriptionsKeyword())
         return true;
     if (value == chaptersKeyword())
         return true;
     if (value == metadataKeyword())
         return true;
 
     return false;
 }
 
+bool TextTrack::isValidKindKeyword(const String& value)
+{
+    if (value == subtitlesKeyword())
+        return true;
+    if (value == captionsKeyword())
+        return true;
+    if (value == descriptionsKeyword())
+        return true;
+    if (value == chaptersKeyword())
+        return true;
+    if (value == metadataKeyword())
+        return true;
+
+    return false;
+}
+
 void TextTrack::setTrackList(TextTrackList* trackList)
 {
     if (!trackList && mediaElement() && m_cues)
         mediaElement()->textTrackRemoveCues(this, m_cues.get());
 
     m_trackList = trackList;
     invalidateTrackIndex();
 }
 
 void TextTrack::setKind(const AtomicString& newKind)
@@ skipping 286 matching lines @@
 void TextTrack::trace(Visitor* visitor)
 {
     visitor->trace(m_cues);
     visitor->trace(m_regions);
     visitor->trace(m_trackList);
     TrackBase::trace(visitor);
     EventTargetWithInlineData::trace(visitor);
 }
 
 } // namespace blink