We have the set up for TextTrack's oncuechange event, calling TextTrack::CueChanged(), implementing the event, etc, but we don't actually emit an event when CueChanged() is called.
I'm not really sure if we need TextTrack::CueChanged(). The oncuechange event only happens when a cue starts being active or stops being active. This means that the cue is being shown on the screen. The place to properly fire this event is in the time marches on algorithm.
Resolving this as invalid since it doesn't match the spec.