Support text track selection in video controls

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 440 matching lines @@
 int TextTrack::trackIndexRelativeToRenderedTracks()
 {
     ASSERT(m_trackList);
 
     if (m_renderedTrackIndex == invalidTrackIndex)
         m_renderedTrackIndex = m_trackList->getTrackIndexRelativeToRenderedTracks(this);
 
     return m_renderedTrackIndex;
 }
 
+bool TextTrack::isRenderable()
+{
+    // A track can be displayed when it's of kind captions or subtitles and hasn't failed to load

[philipj_slow, 2015/05/05 14:36:57]

I guess this means that if the readinessState is NotLoaded and one tries to
enable the track, the next time one opens the menu that track will simply be
gone?

[fs, 2015/05/05 15:32:44]

Yes. Optionally I suppose one could "gray it out" or similar (it's pretty
annoying with things you can interact with but which doesn't do anything...) UI
issue really though.

[srivats, 2016/02/23 01:39:27]

Should we just exclude the NotLoaded tracks from being displayed?

[philipj_slow, 2016/03/01 11:21:04]

I think what you have now in the other CL seems to work well. We can't exclude
NotLoaded tracks, because that could be all of them!

+    if ((kind() == captionsKeyword() || kind() == subtitlesKeyword()) && readinessState() != FailedToLoad)
+        return true;
+    return false;
+}
+
 const AtomicString& TextTrack::interfaceName() const
 {
     return EventTargetNames::TextTrack;
 }
 
 ExecutionContext* TextTrack::executionContext() const
 {
     HTMLMediaElement* owner = mediaElement();
     return owner ? owner->executionContext() : 0;
 }
@@ skipping 17 matching lines @@
 {
     visitor->trace(m_cues);
     visitor->trace(m_activeCues);
     visitor->trace(m_regions);
     visitor->trace(m_trackList);
     TrackBase::trace(visitor);
     EventTargetWithInlineData::trace(visitor);
 }
 
 } // namespace blink