Add rowBytes to createTestingOnlyBackendTexture

This is pulled out of:

https://skia-review.googlesource.com/c/skia/+/151983 (Test YUV images in DDL)

The YUV images seem to like to have row padding.

Change-Id: I517d2b63678beeafef88f86148fca15862176780
Reviewed-on: https://skia-review.googlesource.com/156367
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
30 files changed