Allow changing the transfer function in xform canvas mode

Used this to test out some theories for different color correction
approaches.

Bug: skia:
Change-Id: I072130733eaea736c9aa129af74887b028f035b4
Reviewed-on: https://skia-review.googlesource.com/69221
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
2 files changed