Extend the image asset provider API to support animated/multi-frame images.
Add a GM based on SkAnimCodecPlayer + animated public domain GIF
(source: https://giphy.com/explore/public-domain).
Bug: skia:
Change-Id: Iaa596e01a7626ca6574db1ebc90632f5a9a02bdc
Reviewed-on: https://skia-review.googlesource.com/159162
Commit-Queue: Florin Malita <fmalita@chromium.org>
Reviewed-by: Mike Reed <reed@google.com>
