Make lines in texel_subset GM be at half pixel offsets

As it stands they're at integers and so snap differently on different
GPUs.

Change-Id: I80b955a728aa590af12d9307ba2c36731d333594
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/268170
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
1 file changed