Bug 1328798 - Enable the no-delete-var rule for eslint and fix the one error spotted by the rule. r=jkt

MozReview-Commit-ID: 5wKobd1ehAu

--HG--
extra : rebase_source : db4ce9ad3e49c589a4f3987a592b8c66548f9ac9

browser/base/content/browser.js

@@ -6664,7 +6664,7 @@ var gIdentityHandler = {
     return this._identityBox = document.getElementById("identity-box");
   },
   get _identityPopupMultiView() {
-    delete _identityPopupMultiView;
+    delete this._identityPopupMultiView;
     return document.getElementById("identity-popup-multiView");
   },
   get _identityPopupContentHosts() {

toolkit/.eslintrc.js

@@ -63,6 +63,9 @@ module.exports = {
     // Disallow the use of debugger
     "no-debugger": "error",
 
+    // Disallow deleting variables
+    "no-delete-var": "error",
+
     // No duplicate arguments in function declarations
     "no-dupe-args": "error",