Bug 1233549 disable the ES3 compressed texture formats for the MacOS assertion problem. This bug is for turning it on if we figure it out from spec.
On some platforms, these formats are not available (Mac), or emulated and therefore useless (Windows with ANGLE). We're going to be proposing that these formats are removed from the core spec, and only offered via the existing compressed_textures_es3 extension. This may mean we end up closing this bug with no action.