At the end of the day this allows you to enjoy WebGL from your DirectX 9.0 graphics card driver and not need to worry about any flaky OpenGL support on Windows. This is somewhat similar to Wine's DirectX implementation where they are doing the opposite of converting Direct3D API calls to OpenGL so that they can run on Linux, Mac OS X, etc.
Google is making the Almost Native Graphics Layer Engine code available under a BSD license, but they're only targeting Windows users with this code and potentially mobile platforms. Mentioned on their blog is, "This requirement isn't a problem on computers running OS X or Linux, where OpenGL is the primary 3D API and therefore enjoys solid support." While that is the case, it's actually an issue first of whether the Linux user has any OpenGL support by an open-source or proprietary driver or if it's broken (like was the case with ATI Catalyst and Lucid, until yesterday). Fortunately for open-source users, as of late the OpenGL ES support in Mesa and Gallium3D has improved a lot.
Those interested in learning more about Google's Almost Native Graphics Layer Engine can read about it on the Chromium Blog.