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As far as I can tell, SRGB gamma and 2.2 gamma dst color
spaces are very common, with all other possibilities
being extremely rare.

We'd like to limit our color correct implementations
to approximations of SRGB and 2Dot2 destinations:
(1) Allows software and gpu to stay in sync.
(2) Avoids code bloat caused by supporting any
    arbitrary representation that can be packed into an
    ICC profile.

To be confident in making this decision, we need some
metrics to help verify our assumptions about the dst color
spaces.

BUG=

Review-Url: https://codereview.chromium.org/2177933002
Cr-Commit-Position: refs/heads/master@{#407675}