Add SkSpecialImage-based methods to SkImageFilter

This is calved off of https://codereview.chromium.org/1695823002/ (Get OffsetImageFilter really working with SkSpecialImages)

GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1757983002

Review URL: https://codereview.chromium.org/1757983002
2 files changed