Convert track-webvtt-tc[000-002] tests to testharness.js

third_party/WebKit/LayoutTests/media/track/track-helpers.js

+function enableAllTextTracks(textTracks) {
+    for (var i = 0; i < textTracks.length; i++) {
+        var track = textTracks[i];
+        if (track.mode == "disabled")
+            track.mode = "hidden";
+    }
+}
+
+function assert_cues_equal(cues, expected) {
+    for (var i = 0; i < cues.length; i++) {
+        assert_equals(cues[i].id, expected[i].id);
+        assert_equals(cues[i].startTime, expected[i].startTime);
+        assert_equals(cues[i].endTime, expected[i].endTime);
+        assert_equals(cues[i].text, expected[i].text);
+    }
+}