These make it easier for clients to create new surface characterizations that differ only a little from an existing surface characterization.
Change-Id: Iebd0b32ae941d3f91427927108d092cb5864b09f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/270444
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>