Some more Metal memory fixes.

* Use buffer rather than texture to create test texture
* Get rid of zombie issue

Bug: skia:8243
Change-Id: I681b7ed5583a3806fd723f608068abf716ad70a3
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/206161
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
2 files changed