In the meantime, they never added support for WebGL2 and MSAA on Framebuffer Objects. Blargh.
"We're collaborating with Dean and the WebKit team to use ANGLE for WebGL's backend in WebKit, which will allow an easy upgrade to WebGL 2.0 on all platforms. Follow https://bugs.webkit.org/show_bug.cgi?id=198948 for updates on the work."