feat: add LabelButton API

lib/browser/api/label-button.js

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