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

Source/core/html/HTMLMediaElement.cpp

Index: Source/core/html/HTMLMediaElement.cpp
diff --git a/Source/core/html/HTMLMediaElement.cpp b/Source/core/html/HTMLMediaElement.cpp
index 5da3170242e3b376ad6168b93b22bce496f9f94f..61cf8d2e938788714fbeefeadf80d20d1871d383 100644
--- a/Source/core/html/HTMLMediaElement.cpp
+++ b/Source/core/html/HTMLMediaElement.cpp
@@ -1209,6 +1209,9 @@ void HTMLMediaElement::textTrackModeChanged(TextTrack* track)
         textTrackAddCues(track, track->cues());
 
     configureTextTrackDisplay(AssumeVisibleChange);
+
+    ASSERT(textTracks()->contains(track));
+    textTracks()->scheduleChangeEvent();
 }
 
 void HTMLMediaElement::textTrackKindChanged(TextTrack* track)