Chromium is an OpenGL implementation.
Unlike other OpenGL implementations, Chromium does not render the OpenGL command stream to a raster image in order to display on-screen.
Instead, it manipulates, and moves the OpenGL command stream to other OpenGL implementations (including even other Chromium implementations).
[1] Chromium provides an infrastructure in which modules, known as SPUs or Stream Processing Units, can be inserted.
The last SPU in a node can choose to either pass it to another local OpenGL implementation, such as a graphics card, or send it over a network to one or more Chromium Servers.