Clean up textTrackDisplayElement utility function

third_party/WebKit/LayoutTests/media/video-controls-captions.html

Index: third_party/WebKit/LayoutTests/media/video-controls-captions.html
diff --git a/third_party/WebKit/LayoutTests/media/video-controls-captions.html b/third_party/WebKit/LayoutTests/media/video-controls-captions.html
index aea44b909edaa7e03608e7acb4e117a89b9c1ecd..63302da979c4decf9ea687cc963556dc3f989bd8 100644
--- a/third_party/WebKit/LayoutTests/media/video-controls-captions.html
+++ b/third_party/WebKit/LayoutTests/media/video-controls-captions.html
@@ -21,11 +21,11 @@ async_test(function(t) {
 
         var track = document.querySelector("track");
         track.onload = t.step_func(function() {
-            assert_equals(textTrackCueElementByIndex(video, 0).innerText, "Lorem");
+            assert_equals(textTrackDisplayElement(video).innerText, "Lorem");
 
             // Captions should not be visible after Off is clicked.
             turnClosedCaptionsOff(video);
-            assert_equals(textTrackCueDisplayElement(video), null);
+            assert_equals(textTrackDisplayElement(video), null);
 
             // Remove DOM node representing the track element.
             track.remove();