Google is switching to its own Root Certificate Authority for issuing its own SSL certificates for securing its web traffic via HTTPS. In the past years, Google has used certificates issued by several companies, with the lastly supplied by GlobalSign and GeoTrust. Google is currently in the process of migrating all services and products from GIAG2 certificates to GTS. This will make it easier to identify authentic Google services, as it was so for GlobalSign, GeoTrust, or any other term.”]
Source: https://gbhackers.com/google-switches-to-own-root-certificate-authority-google-trust-services/