Opera Presto is the layout engine at the heart of the old Opera browser. Opera Software used Presto between Opera 7 and Opera 14 and replaced Presto with Blink, Chrome's layout engine, in Opera 15, released in May 2013.
According to information provided in the repositories, the leaked source code is for version 12.15 of the Opera engine. Opera has not developed the Presto engine in past years, and most likely, this is an outdated technology. Unlike Google, Mozilla, Apple, and Microsoft, who open-sourced some parts of their browsers' source code, Opera never open-sourced any part of the Presto engine.