The #ifdef around the test of the accelerated compositing flag when creating a WebGLRenderingContext (WebCore/html/HTMLCanvasElement.cpp) should be generalized. Currently only the Chromium port ignores the flag, meaning that WebGL works as long as it is enabled, regardless of the sense of the accelerated compositing run-time flag. fishd@chromium suggested 3D_CANVAS_REQUIRES_ACCELERATED_COMPOSITING. Need to think through interactions with the USE(ACCELERATED_COMPOSITING) compile-time flag and ensure that WebGL doesn't get unexpectedly enabled for ports in situations they don't expect it.
Seems the flags have changed significantly. Maybe a new bug could be filed if this is an issue.