Use ES3 in iOS test harness

Bug: skia:
Change-Id: I365c82a058c97e8741ee91e999cb6faab5a5ecf5
Reviewed-on: https://skia-review.googlesource.com/c/175422
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
2 files changed