Guard ANGLE and MESA instead of defining them as native when unsupported.

Since we've added "angle" to the default list of configs we've been running
kNative_GLContextType tests twice in DM, once for the real native, once for
angle.  This pointlessly doubles the GPU critical path in DM.  Whoops.

NOTREECHECKS=true

BUG=skia:
R=bsalomon@google.com, mtklein@google.com

Author: mtklein@chromium.org

Review URL: https://codereview.chromium.org/471063002
1 file changed