Finish supporting decoding opaque to non-opaque
When decoding to 565 or Gray, allow the client to incorrectly ask for premul.
When checking whether it's possible to decode to 565, return whether the
source is opaque.
In DM, allow decoding to 565 or Gray, even if the client also asked for premul.
This fixes a bug introduced in crrev.com/1999593003 when we stopped ever
requesting Opaque, resulting in us not testing 565 or Gray.
BUG=skia:4616
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=1996993003
Review-Url: https://codereview.chromium.org/1996993003
4 files changed