DrawContext's isGammaCorrect now just based on presence of color space.
Next change will remove the function and flag entirely, but I wanted to
land this separately. This alters a few GMs in srgb/f16 mode, generally
those that are creating off-screen surfaces in ways that were somewhat
lossy before. No unexplained changes.
BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2186633002
Review-Url: https://codereview.chromium.org/2186633002
9dc935fa11