Add LayoutManager/BoxLayout APIs

lib/browser/api/box-layout.js

@@ -0,0 +1,15 @@
+'use strict'
+
+const electron = require('electron')
+
+const {LayoutManager} = electron
+const {BoxLayout} = process.atomBinding('box_layout')
+
+Object.setPrototypeOf(BoxLayout.prototype, LayoutManager.prototype)
+
+BoxLayout.prototype._init = function () {
+  // Call parent class's _init.
+  LayoutManager.prototype._init.call(this)
+}
+
+module.exports = BoxLayout