WIP: runtime switch for how to interpret SkColor -vs- srgb

Still very conflicted about the "right" way to proceed with this, but thought I'd experiment with a runtime flag, so we can practice seeing SKPs in various stages of "srgb correctness".

Other aspects to either fix, or at least provide runtime switches for:

- untagged images
- gradients
- colorshader
- drawVertices

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1891013002

TBR=

Review URL: https://codereview.chromium.org/1891013002
2 files changed