Bug 1635098 - Allow nullish coalescing and optional chaining operators in newtab jsm code r=k88hudson

Include babel plugins to allow unit testing of files using the operators.
Reverts "Bug 1635054 - stop using ?. operator in newtab download manager code, r=aryx"

Differential Revision: https://phabricator.services.mozilla.com/D73739

Author: Mardak

browser/components/newtab/karma.mc.config.js

@@ -161,6 +161,8 @@ module.exports = function(config) {
                         replace: true,
                       },
                     ], // require("babel-plugin-jsm-to-commonjs")
+                    "@babel/plugin-proposal-nullish-coalescing-operator",
+                    "@babel/plugin-proposal-optional-chaining",
                   ],
                 },
               },

browser/components/newtab/lib/DownloadsManager.jsm

@@ -35,9 +35,7 @@ this.DownloadsManager = class DownloadsManager {
   }
 
   formatDownload(download) {
-    let { referrerInfo } = download.source;
-    let referrer = (referrerInfo && referrerInfo.originalReferrer) || null;
-    referrer = (referrer && referrer.spec) || null;
+    let referrer = download.source.referrerInfo?.originalReferrer?.spec || null;
     return {
       hostname: new URL(download.source.url).hostname,
       url: download.source.url,

browser/components/newtab/package-lock.json

@@ -18,6 +18,8 @@
   },
   "devDependencies": {
     "@babel/core": "7.8.4",
+    "@babel/plugin-proposal-nullish-coalescing-operator": "7.8.3",
+    "@babel/plugin-proposal-optional-chaining": "7.9.0",
     "@babel/preset-react": "7.8.3",
     "acorn": "7.1.0",
     "babel-loader": "8.0.6",