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

browser/base/content/browser.js

@@ -6664,8 +6664,8 @@ var gIdentityHandler = {
     return this._identityBox = document.getElementById("identity-box");
   },
   get _identityPopupMultiView() {
-    delete _identityPopupMultiView;
-    return document.getElementById("identity-popup-multiView");
+    delete this._identityPopupMultiView;
+    return this._identityPopupMultiView = document.getElementById("identity-popup-multiView");
   },
   get _identityPopupContentHosts() {
     delete this._identityPopupContentHosts;

toolkit/.eslintrc.js

@@ -66,6 +66,9 @@ 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",