Add static helper to bind touch bar to window

lib/browser/api/browser-window.js

@@ -1,6 +1,7 @@
 'use strict'
 
-const {ipcMain, TouchBar} = require('electron')
+const electron = require('electron')
+const {ipcMain} = electron
 const {EventEmitter} = require('events')
 const {BrowserWindow} = process.atomBinding('window')
 const v8Util = process.atomBinding('v8_util')
@@ -196,23 +197,8 @@ Object.assign(BrowserWindow.prototype, {
   capturePage (...args) {
     return this.webContents.capturePage(...args)
   },
-
-  // TouchBar API
   setTouchBar (touchBar) {
-    // This property is set from within TouchBar
+    electron.TouchBar._setOnWindow(touchBar, this)
-    if (this._touchBar != null) {
-      this._touchBar._removeFromWindow(this)
-    }
-
-    if (touchBar == null) {
-      this._setTouchBarItems([])
-      return
-    }
-
-    if (Array.isArray(touchBar)) {
-      touchBar = new TouchBar(touchBar)
-    }
-    touchBar._addToWindow(this)
   }
 })
 

lib/browser/api/touch-bar.js

@@ -3,6 +3,24 @@ const {EventEmitter} = require('events')
 let itemIdIncrementor = 1
 
 class TouchBar extends EventEmitter {
+
+  // Bind a touch bar to a window
+  static _setOnWindow (touchBar, window) {
+    if (window._touchBar != null) {
+      window._touchBar._removeFromWindow(window)
+    }
+
+    if (touchBar == null) {
+      window._setTouchBarItems([])
+      return
+    }
+
+    if (Array.isArray(touchBar)) {
+      touchBar = new TouchBar(touchBar)
+    }
+    touchBar._addToWindow(window)
+  }
+
   constructor (items) {
     super()