[sksg] Use luminance coefficients from SkColorData.h

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Change-Id: I2dc48f3d4e1ee1b873bd41ede5168191f69bde30
Reviewed-on: https://skia-review.googlesource.com/c/194427
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>
1 file changed