Add some swizzle checks to vulkan backend

Bug: skia:
Change-Id: I9f5a5c1fda9cf26fc6479e1cd6d0e981e6991c8e
Reviewed-on: https://skia-review.googlesource.com/16426
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
2 files changed