add bench for colorfilter-mixer

Change-Id: Iab8a25b086a492838931b0fab2d6239ae975b435
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/204640
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
Auto-Submit: Mike Reed <reed@google.com>
1 file changed