Ported media stream track enable-disable test to content module.

content/test/data/media/webrtc_test_utilities.js

Index: content/test/data/media/webrtc_test_utilities.js
diff --git a/content/test/data/media/webrtc_test_utilities.js b/content/test/data/media/webrtc_test_utilities.js
index 1377ca8c1ba2ce106dfdce90b62636bc94ca3df3..249a9708d1fe9855bc7d90bee2e831207033c634 100644
--- a/content/test/data/media/webrtc_test_utilities.js
+++ b/content/test/data/media/webrtc_test_utilities.js
@@ -70,12 +70,11 @@ function waitForVideoToStop(videoElement) {
   detectVideoStopped(videoElement, function () { eventOccured(); });
 }
 
-function waitForConnectionToStabilize(peerConnection) {
-  addExpectedEvent();
+function waitForConnectionToStabilize(peerConnection, callback) {
   var waitForStabilization = setInterval(function() {
     if (peerConnection.signalingState == 'stable') {
       clearInterval(waitForStabilization);
-      eventOccured();
+      callback();
     }
   }, 100);
 }