Add RAW decoding into Skia.

TBR=reed@google.com

BUG=skia:

(Based on the work from ebrauer in https://codereview.chromium.org/1459473007)
(Based on the work from adaubert in https://codereview.chromium.org/1494003003)
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1520403003

Review URL: https://codereview.chromium.org/1520403003
16 files changed