Chromium Embedded Framework
From Valve Developer Community
In relation to Valve
The Steam client on Windows and OS X uses a customized version of CEF to render web content.
The Source code for Valve's usage of the Chromium Embedded Framework (and Chromium) can be downloaded as a ZIP archive (783 MB, 24th April 2012). A patch for revision 465 of the CEF codebase is available on pastebin (280 KB) that will apply Valve's changes.