This allows a subsequent CL to introduce windows support by directly calling an ANGLE dll. For golang/go#9306 Change-Id: I7dbe8f2b77b9e2c744f0d848f716ee4448916fe7 Reviewed-on: https://go-review.googlesource.com/17674 Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>