updateBackendTexture uses GrSurfaceContext to write pixmaps.

Bug: skia:11786

Change-Id: I1c70b7152a69b2bb976aec2ed1dc9d5f96cad7ab
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/348185
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
7 files changed