When creating emptyp MipMap proxies, don't instantiate them immediately.

This chnages makes it match how we handle non mipped proxies where we
don't actually instantiate them until we need to.

Bug: skia:
Change-Id: Id0c50eefce43ef1458a3ff0bb1881a817b045279
Reviewed-on: https://skia-review.googlesource.com/106966
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
8 files changed