The ANGLE project in ThirdParty/ANGLE contains (nearly) all of the validation needed to make conformant WebGL 1.0 and 2.0 implementations with minimal code; largely just wrapping ANGLE's objects as WebGLObjects. ANGLE is supported on all of the platforms used by WebKit's ports - or, at least, should be. Patches will be welcomed into the ANGLE project supporting it on more platforms.
This meta-bug tracks using ANGLE as the backend for WebKit's WebGL implementation, and ideally, removal of GraphicsContext3DOpenGL and GraphicsContext3DOpenGLES.
It would be great to have Webkit/Safari support Webgl like other browsers. I think great progress has been made. Looking forward to seeing this land in Safari sometime soon.