Add "change" and "removetrack" events to TextTrackList.

LayoutTests/media/track/track-remove-track-expected.txt

Index: LayoutTests/media/track/track-remove-track-expected.txt
diff --git a/LayoutTests/media/track/track-remove-track-expected.txt b/LayoutTests/media/track/track-remove-track-expected.txt
new file mode 100644
index 0000000000000000000000000000000000000000..c8e4fcd89ed5c073215ef6e84a980aa4c736acf4
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+++ b/LayoutTests/media/track/track-remove-track-expected.txt
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+Tests that the 'removetrack' event is fired when a TextTrack is removed.
+
+** Test a TextTrack created for a <track> element.
+RUN(trackElement = document.createElement('track'))
+RUN(video.appendChild(trackElement))
+RUN(trackElement.src = 'captions-webvtt/tc004-webvtt-file.vtt')
+RUN(trackElement.track.mode = 'hidden')
+EXPECTED (video.textTracks.length == '1') OK
+EVENT(removetrack)
+EXPECTED (event.target == '[object TextTrackList]') OK
+EXPECTED (event instanceof window.TrackEvent == 'true') OK
+EXPECTED (event.track == '[object TextTrack]') OK
+
+END OF TEST
+