Currently, Skia always uploads GPU textures at full resolution. This
change allows us to pass a pre-scale mip level to the
deferred texture image logic, which causes us to pre-scale the image
to the given mip level, and upload that mip level instead of the full
image.
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2007113008
Review-Url: https://codereview.chromium.org/2007113008