refactor: add promise helper and change whenReady to be native impl (#13115)

* Add promise helper and change whenReady to be native impl

* remove commented code

* add GetInner helper to dedupe promise code

* add Promise.reject helper to be consistent with JS

* fix linting

* update promise impl per feedback

* remove param name from unused isolate

* Use non-depreceated resolvers for promises

* Add thread dchecks for promise helper, intiialize promise pointer to nullptr

lib/browser/api/app.js

@@ -12,30 +12,12 @@ const {deprecate, Menu} = electron
 const {EventEmitter} = require('events')
 
 let dockMenu = null
-let readyPromise = null
 
 // App is an EventEmitter.
 Object.setPrototypeOf(App.prototype, EventEmitter.prototype)
 EventEmitter.call(app)
 
 Object.assign(app, {
-  whenReady () {
-    if (readyPromise !== null) {
-      return readyPromise
-    }
-
-    if (app.isReady()) {
-      readyPromise = Promise.resolve()
-    } else {
-      readyPromise = new Promise(resolve => {
-        // XXX(alexeykuzmin): Explicitly ignore any data
-        // passed to the event handler to avoid memory leaks.
-        app.once('ready', () => resolve())
-      })
-    }
-
-    return readyPromise
-  },
   setApplicationMenu (menu) {
     return Menu.setApplicationMenu(menu)
   },