Blacklist Metal on macOS 10.12

Metal has an extremely elevated crash rate on macOS 10.12, across all
GPU vendors.

Bug: 963000
Change-Id: I206f3035d9a1bbf0aa1bb1fefe23278542c58e03
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1614464
Reviewed-by: Eric Karl <ericrk@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Commit-Queue: ccameron <ccameron@chromium.org>
Cr-Commit-Position: refs/heads/master@{#660564}
6 files changed