Hide the CC button for <audio> with <track>s

LayoutTests/media/media-controls.js

 var captionsButtonElement;
 var captionsButtonCoordinates;
 
 function mediaControlsElement(first, id)
 {
     for (var element = first; element; element = element.nextSibling) {
         // Not every element in the media controls has a shadow pseudo ID, eg. the
         // text nodes for the time values, so guard against exceptions.
         try {
             if (internals.shadowPseudoId(element) == id)
@@ skipping 61 matching lines @@
         if (!displayElement)
             throw "There are not " + cueNumber + " text track cues visible";
     }
 
     return displayElement;
 }
 
 function testClosedCaptionsButtonVisibility(expected)
 {
     try {
-        captionsButtonElement = mediaControlsElement(internals.shadowRoot(video).firstChild, "-webkit-media-controls-toggle-closed-captions-button");
-        captionsButtonCoordinates = mediaControlsButtonCoordinates(video, "toggle-closed-captions-button");
+        captionsButtonElement = mediaControlsElement(internals.shadowRoot(mediaElement).firstChild, "-webkit-media-controls-toggle-closed-captions-button");
+        captionsButtonCoordinates = mediaControlsButtonCoordinates(mediaElement, "toggle-closed-captions-button");
     } catch (exception) {
         consoleWrite("Failed to find a closed captions button or its coordinates: " + exception);
         if (expected)
             failTest();
         return;
     }
 
     consoleWrite("");
     if (expected == true) {
-        consoleWrite("** Caption button should be visible and enabled because we have a captions track.");
+        consoleWrite("** Caption button should be visible and enabled.");
         testExpected("captionsButtonCoordinates[0]", 0, ">");
         testExpected("captionsButtonCoordinates[1]", 0, ">");
         testExpected("captionsButtonElement.disabled", false);
     } else {
-        consoleWrite("** Caption button should not be visible as there are no caption tracks.");
+        consoleWrite("** Caption button should not be visible.");
         testExpected("captionsButtonCoordinates[0]", 0, "<=");
         testExpected("captionsButtonCoordinates[1]", 0, "<=");
     }
 }
 
 function clickCCButton()
 {
     consoleWrite("*** Click the CC button.");
     eventSender.mouseMoveTo(captionsButtonCoordinates[0], captionsButtonCoordinates[1]);
     eventSender.mouseDown();
     eventSender.mouseUp();
 }