Implement getTransferFunction

Supports V4 parametric curves, and V2 linear/gamma curves. Curve fitting
of V2 tables is left as an exercise for the reader.

Change-Id: Ide9756631dc407a8b174680166d3b2ce71087387
Reviewed-on: https://skia-review.googlesource.com/92104
Reviewed-by: Mike Klein <mtklein@chromium.org>
5 files changed