Bug 1246842 - Rework previous commit to not used deprecated arguments.callee r=cpearce

MozReview-Commit-ID: DFWNOGN0FyY

--HG--
extra : transplant_source : %1E%0D%0E%F7%EB%AE%10%40%D6%C2%3F%03%EC%16%98%91Z%60%D8%20

dom/media/mediasource/test/mediasource.js

@@ -53,8 +53,8 @@ function range(start, end) {
 
 function once(target, name, cb) {
   var p = new Promise(function(resolve, reject) {
-    target.addEventListener(name, function() {
-      target.removeEventListener(name, arguments.callee);
+    target.addEventListener(name, function onceEvent() {
+      target.removeEventListener(name, onceEvent);
       resolve();
     });
   });

dom/media/test/manifest.js

@@ -1357,8 +1357,8 @@ function removeNodeAndSource(n) {
 
 function once(target, name, cb) {
   var p = new Promise(function(resolve, reject) {
-    target.addEventListener(name, function() {
-      target.removeEventListener(name, arguments.callee);
+    target.addEventListener(name, function onceEvent() {
+      target.removeEventListener(name, onceEvent);
       resolve();
     });
   });