[skif] Mark AutoSurface's device as immutable when snapping

For GPU-backed special images, this shouldn't make a difference, but
it avoids a copy when a raster-backed SkSpecialImage is viewed as an
SkImage or SkShader.

Change-Id: I4f81aebf2aef51e08b00c089b68765346c51d03b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/787936
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
1 file changed