[yrio]

Dart is used for AdWords [0] and AdSense [1]. Both of which account for 89% of Google's revenue.

It's also used for Google's internal CRM (Greentea), and Google Fiber.

[0] http://news.dartlang.org/2016/03/the-new-adwords-ui-uses-dar...

[1] http://news.dartlang.org/2016/10/google-adsense-angular-dart...