SkWebpEncoder: Support animated image encoding

This change adds support for animated WebP image encoding, which makes
it possible to serve sanitized animated image in ChromeOS WebUI.

For detailed background: go/avatars-from-cloud

Bug: b/243200556
Change-Id: I53c545672cec00ad88046a96eca0acdefc1a6b7a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/572935
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: Yue Li <updowndota@google.com>
Commit-Queue: Yue Li <updowndota@google.com>
Reviewed-by: Leon Scroggins <scroggo@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
5 files changed