Fix ODR violation in Metal code.

In places where we use GR_METAL_SDK_VERSION to determine the contents of
a class, it's important to consistently #include the header which sets
the value of GR_METAL_SDK_VERSION.

Change-Id: Ic4824ff36c982d3493ebec03dd38465bb90b287a
Bug: skia:12513
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/461836
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
2 files changed