Add lerping to skcms_eval_curve

Change-Id: I17eaf5f80623904feb3d50db46a288936acb1863
Reviewed-on: https://skia-review.googlesource.com/128561
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
27 files changed