Extend blendmodes bench to time sprites

Change-Id: I3801e869d8a2e177dae108a494a221d502c3caaf
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/425182
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
1 file changed