[skotty] Add Json DM source

Generates a filmstrip with evenly distributed frames for a Skotty animation.

TBR=
Change-Id: Ia89e0d65d59fd5ab4ef221a231e9b3e0c033828a
Reviewed-on: https://skia-review.googlesource.com/90025
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>
7 files changed