Freon does away with the rest of its X11 Server dependencies and in the process is aiming to provide better performance, reduced power consumption, and a smaller Chrome OS binary.
Within Freon, there technically isn't a display server. Under the Freon driver model, the Chrome browser talks directly to the kernel's DRM/KMS APIs and is also communicating directly with OpenGL ES for the 3D drawing functionalities. With Chrome OS 41 this functionality is mostly for the Intel Chromebooks while the various Samsung ARM Chromebooks sohould receive similar treatment in a later release (from messages thus far, it looks to be around Chrome OS 43). The initial Freon-supported devices include the Chromebook Pixel, Acer C720, ASUS Chromebox, HP Chromebox, LG Chromebase, Acer Chromebox, and Dell Chromebox. The initial limitations are due to being dependent upon DRM/KMS support by the graphics hardware.
Among the benefits of Freon is supporting hardware overlays for compositing, partial screen update support, zero-copy texture uploads, external display device improvements, and reduced input in the latency stack. Some of this Freon graphics stack work was shared via this Google+ post by François Beaufort of Google.
Given the limited scope of Chrome OS, having not previously exposed X11 support to clients, and mostly being just a full-screen browser, switching to Freon is relatively easy and can be incredibly lean given the requirements by talking directly to the KMS/DRM and GLES APIs. As part of the Freon graphics stack is Frecon, a basic console for Chrome OS implemented against the KMS API.
Aside from Chrome/Chromium continuing to run on X11 when it comes to non-ChromeOS Linux desktops, there's still work on allowing Chrome OS to run under Wayland and Mir via the Ozone abstraction layer with Ozone-Mir and Ozone-Wayland.