On macOS, how do I change my default "mailto" client to the Google Web App?

On Mac OS X, when you click on an email ("mailto") link, by default Apple Mail opens the new message window. What if you want the Connect Google Web App to open and send the new message?

To change the default email client from Apple Mail to the Google Web App (GWA) in Google Chrome, you need to do 2 things:

1) In Apple Mail, set Google Chrome as the default email reader:
- open Apple Mail and select Preferences from the Mail menu
- on the General tab, find Default email reader and click on the drop-down menu
- click Select... 
- in the "Applications" list, click Google Chrome
- click the Select button
- close the Preferences window

2) Allow mail.google.com to open all email links:
- open the Google Chrome browser and log into your Connect account using the GWA
- click the Handler icon (2 overlapping diamonds) near the right end of the address bar at the top of the window
- click Allow to the question "Allow mail.google.com to open all email links?"
- click Done

Now, clicking "mailto" links will automatically open the email draft in GWA if you are logged into GWA using Chrome. If you are not logged into GWA/Chrome, Chrome will open and ask you to log into GWA.