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Add an API to extract a color transform lookup table in BGRA format, with
(z,y,x) sampling order (B changes the slowest, R the fastest).

See r314425 for speed results, noting that qcms_chain_transform takes 8ms
for a 32-cube since floating-point is used to compute the color transform
to maintain transform precision.

The float data produced by qcms_chain_transform() is stored in the output
in BGRA order (color components are rounded to the nearest 8-bit integer)
with time cost 0.000031 secs. Note that if the data needed re-indexing to
(x,y,z) sampled, RGBA order on writing to the output, the time cost would
be 0.00056 secs (18 times slower) [1].

[1] See r314425 review comments about sampling and pixel order.

BUG=443863

Review URL: https://codereview.chromium.org/892413005

Cr-Commit-Position: refs/heads/master@{#315188}