Add "none" option for --pr, to force software path renderer

There was no way to get this behavior without triggering an error before.

Bug: skia:
Change-Id: Id9cb9090e47226dadad0032f06ec205dd2538dcc
Reviewed-on: https://skia-review.googlesource.com/37001
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
1 file changed