Bug 1264434 - Use String.prototype.includes in browser_webconsole_bug_597136_network_requests_from_chrome.js. r=bgrins

String.prototype.contains was removed from Firefox 48 completely after
it was renamed to String.prototype.includes. The test includes a
call to .contains() which is triggered whenever random JavaScript
error occurs during the test (hence the intermittency).

MozReview-Commit-ID: 7nbRm94JM7O

--HG--
extra : rebase_source : e969bc1ad46120509deec31066ea63ebbb7de9c9

devtools/client/webconsole/test/browser_webconsole_bug_597136_network_requests_from_chrome.js

@@ -16,7 +16,7 @@ var listener = {
   observe: function (subject) {
     if (subject instanceof Ci.nsIScriptError &&
         subject.category === "XPConnect JavaScript" &&
-        subject.sourceName.contains("webconsole")) {
+        subject.sourceName.includes("webconsole")) {
       good = false;
     }
   }