How to have Chrome use Gmail for mailto: links without an extension!

If you use Google Chrome and Gmail, and hate it when you click an email link and Apple Mail or Outlook opens instead of just using Gmail, here is how to get Gmail handling emails without the need for any extension or add-ons, it’s a built-in feature to Chrome!

UPDATE: This is now a built in feature to Gmail, just log in and a bar should appear at the top of Chrome!