More SkImage_GpuYUV updates

Bug: skia:7901
Change-Id: If5f747ff95c65ac95cfed8c1282cc08019d8006a
Reviewed-on: https://skia-review.googlesource.com/c/160024
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
7 files changed