Fix cases of variable shadowing in test code.

If we manage to fix all the existing cases of variable shadowing, we
could enable -Wshadow.

Change-Id: I571931e01b0b95d85a7b566fc785ac219e8e731f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/438697
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Tyler Denniston <tdenniston@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
6 files changed