Support text track selection in video controls

Source/core/html/track/TextTrack.cpp

Index: Source/core/html/track/TextTrack.cpp
diff --git a/Source/core/html/track/TextTrack.cpp b/Source/core/html/track/TextTrack.cpp
index 3916eb7159ac8f3b29f831a64debde7c48ff5597..e87191fa7bcf03bd720931d2c6c26353efbc52dd 100644
--- a/Source/core/html/track/TextTrack.cpp
+++ b/Source/core/html/track/TextTrack.cpp
@@ -458,6 +458,14 @@ int TextTrack::trackIndexRelativeToRenderedTracks()
     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;