Split apart creation of the callback contexts and the backend textures
This allows the texture upload to be done separately on the
gpu-thread
Add a backendFormat member to the promise image callback context
This allows the promise images to be created in CreatePromiseImages
before the backend textures have been created (i.e., the backend
textures can now be created on the gpu-thread so we have no
guarantee they will be available when the SKP is being reinflated
w/ promise images)
Change-Id: I1e21385e450a5ef27dd6950d9d6aee737aa7515d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/270939
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
923181b6e3