Add a SkMixerColorFilter GM

Change-Id: I26382a669601f2bebb1f95e56eab2ad3718db4b9
Reviewed-on: https://skia-review.googlesource.com/c/193165
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
2 files changed