Bug 1249144 - [webext] fix sorting collected frame details in webNavigation tests. r=kmag

MozReview-Commit-ID: ay5fGRGSpW

--HG--
extra : transplant_source : %AC%05%86w%18%F7Q%0B%F4%BA%7Ci%F5k.%E7%80%0Ak%B9

browser/components/extensions/test/browser/browser_ext_webNavigation_getFrames.js

@@ -139,7 +139,11 @@ add_task(function* testWebNavigationFrames() {
      "number of frames found should equal the number onCompleted events collected");
 
   // ordered by frameId
-  let sortByFrameId = (el) => el ? el.frameId : -1;
+  let sortByFrameId = (el1, el2) => {
+    let val1 = el1 ? el1.frameId : -1;
+    let val2 = el2 ? el2.frameId : -1;
+    return val1 - val2;
+  };
 
   collectedDetails = collectedDetails.sort(sortByFrameId);
   getAllFramesDetails = getAllFramesDetails.sort(sortByFrameId);