skcms_EnsureUsableAsDestinationWithSingleCurve

Like skcms_EnsureUsableAsDestination, but also guarantees that the
resulting profile has a single parametric transfer function. Updated the
error metric (from skcms_BestSingleCurve) to optimize for round-trip
error, like other places in skcms.

Change-Id: Iedb2a72da398f464010547d314fe099b8da6b920
Reviewed-on: https://skia-review.googlesource.com/123424
Auto-Submit: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Mike Klein <mtklein@chromium.org>
4 files changed