If you use Google Tag Manager to add and update your site tags, now you can quickly and easily verify ownership of your site in Webmaster Tools using the container snippet code.
Here’s how it’s done:
1. On the Webmaster Tools home page, click Manage site for the site you’d like to verify, then select Verify this site. If you haven’t added the site yet, you can click the Add a site button in the top right corner.... Read more on Google Tag Manager Verification Support