Sync audio/video/text track-related interfaces with the specs

Source/core/html/track/TextTrackCueList.idl

Index: Source/core/html/track/TextTrackCueList.idl
diff --git a/Source/core/html/track/TextTrackCueList.idl b/Source/core/html/track/TextTrackCueList.idl
index 6ea59a645cd1a5fff58e3b0a53ca6df14a44fe69..a65101b83fe98c386a512424e3c926001f5cf429 100644
--- a/Source/core/html/track/TextTrackCueList.idl
+++ b/Source/core/html/track/TextTrackCueList.idl
@@ -23,11 +23,13 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+// https://html.spec.whatwg.org/#texttrackcuelist
+
 [
     WillBeGarbageCollected,
 ] interface TextTrackCueList {
     readonly attribute unsigned long length;
-    getter TextTrackCue item(unsigned long index);
-    TextTrackCue getCueById(DOMString id);
+    // TODO(philipj): This getter should be anonymous.
+    [Measure] getter TextTrackCue item(unsigned long index);
+    TextTrackCue? getCueById(DOMString id);
 };
-