Slight variation on https://skia-review.googlesource.com/c/7346/,
which had to be reverted. This version also changes the non-mip
upload path to use a GrTextureProxy. Hopefully this doesn't trigger
the same perf regression that we saw last time.
BUG=skia:
Change-Id: Ic99bdd93904089942fb680c3af9c4c36310074c0
Reviewed-on: https://skia-review.googlesource.com/9892
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
ed182d7c90