Add new SkSourceGammaTreatment enum, used in situations like mipmap construction, where we need to know if we should respect (vs. ignore) the gamma encoding of sRGB tagged images. Plumb that extensively.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2037413002

Review-Url: https://codereview.chromium.org/2037413002
54 files changed