Per guidance from the Skia team, enabling the Metal backend without any of the OpenGL related code in the binary should be possible by setting the skia_use_gl flag to false after any Skia version past fb27c9a25f. The Metal test bots already use this configuration.

While dropping support for OpenGL will mean leaving behind older and/or un-updated hardware, this issue tracks quantifying the binary size savings from a Metal only build.