Return GrBackendTexture from SkPromiseImageTexture by value.

Makes it simpler to call methods that update the internal ref counted
state.

Change-Id: Iecefab2c14ff13eae2fa34eafdcc7e031b3c85b0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/320957
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
1 file changed