Add SkAutoPixmapStorage::detachPixelsAsData()

Allows passing pixels ownership to clients.

BUG=skia:4896
R=reed@google.com
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1662353002

Review URL: https://codereview.chromium.org/1662353002
2 files changed