Make feature structs on GrVkBackendContext const.

Change-Id: I6655c2458a4a9b007cb3d5e100f5368697a0f6bb
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/218547
Commit-Queue: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
Auto-Submit: Greg Daniel <egdaniel@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
1 file changed