Implement BrowserPluginGuestDelegate::CreateNewGuestWindow for nativeWindowOpen

lib/browser/api/browser-window.js

@@ -36,8 +36,9 @@ BrowserWindow.prototype._init = function () {
                                                 frameName) => {
     v8Util.setHiddenValue(webContents, 'url-framename', {url, frameName})
   })
+
   // Create a new browser window for the native implementation of
-  // "window.open"(sandbox mode only)
+  // "window.open", used in sandbox and nativeWindowOpen mode
   this.webContents.on('-add-new-contents', (event, webContents, disposition,
                                             userGesture, left, top, width,
                                             height) => {