More robust check for sRGB gamma tables

This is in response to a UMA showing that 5% dst gammas are
unidentified tables.  We want to see if some of these tables
should be marked as sRGB.
https://uma.googleplex.com/p/chrome/histograms?endDate=latest&dayCount=1&histograms=Blink.ColorSpace.Destination&fixupData=true&showMax=true&filters=isofficial%2Ceq%2CTrue&implicitFilters=isofficial

This check is not fast.  If we find that it doesn't help
us recognize sRGB curves, we should delete it.

BUG=skia:5656
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2263233003

Review-Url: https://codereview.chromium.org/2263233003
1 file changed