Add helper to create self-managed BackendTexture-backed SkSurface for
tests using MBET.
GrGpu::createTestingOnlyBackendRenderTarget supports protected.
Make SkSurfaceCharacterization tests use self-managed SkSurface
factories and a use case of MakeFromBackendTextureAsRenderTarget is
removed.
Use self-managed BackendTexture-backed SkSurface factory in DM sinks and
in fm.
Bug: skia:9832
Change-Id: I0c1dc49697f8b3c942864e18b9112a3552f431ba
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/323559
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
