Make Metal render loop more stable Bug: skia:8737 Change-Id: Ib825e5f0c9502692cbecc60fbb68d0d1a2bc635f Reviewed-on: https://skia-review.googlesource.com/c/skia/+/208672 Auto-Submit: Jim Van Verth <jvanverth@google.com> Reviewed-by: Brian Salomon <bsalomon@google.com> Commit-Queue: Brian Salomon <bsalomon@google.com>