First implementation of GrTextureRenderTarget.

Change-Id: I0e6bc516eb43e7f7062f9d19e7ef8093324b551d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/233997
Commit-Queue: Stephen White <senorblanco@chromium.org>
Reviewed-by: Greg Daniel <egdaniel@google.com>
4 files changed