Google domains' DNS doesn't support ALIAS/ANAME record to apex domain (also naked domain), but it supports domain forwarding to a subdomain from an apex domain.
Let's set this up.
In this example, we use the following records as a sample:
CDN Raw Hostname:
1. Log in to the Google Domains Control Panel
2. Navigate to [My domains]
3. Click the [Manage] button on your domain
4. Navigate to [Website] menu
5. Click [Set up forwarding]
6. Set up like below:
a) Input the naked domain name to the "Forward from" field
b) Input the URL of the www-prefixed domain name.
c) Click the [Forward] button to save changes
7. Domain forwarding has been added.
Let's access your naked domain with your web browser and check that the domain is forwarding correctly.
Here is a sample command with a URL and its result:
curl --head http://example.com
HTTP/1.1 301 Moved Permanently
Date: Wed, 19 Jun 2019 09:51:10 GMT
Content-Type: text/html; charset=UTF-8