[fiddle] Add simple animation support.

BUG=skia:

Change-Id: I6453afb1fe18e210d3c505b56777b8b19501ca2f
Reviewed-on: https://skia-review.googlesource.com/13810
Commit-Queue: Joe Gregorio <jcgregorio@google.com>
Reviewed-by: Hal Canary <halcanary@google.com>
5 files changed