Add caps files for metal

Bug: skia:
Change-Id: I8e7488320d4237cf67d6ebeaad319d3de75b67e6
Reviewed-on: https://skia-review.googlesource.com/27741
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
6 files changed