Add iOS Metal Test job.

Bug: skia:8230
Change-Id: I500905b9e3db46ab775cf56a433de0bb17ef232c
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/146400
Commit-Queue: Greg Daniel <egdaniel@google.com>
Auto-Submit: Ben Wagner <benjaminwagner@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
2 files changed