SkColorSpaceXformSteps improvements and tests

Added some helper functions and put the booleans in a nested struct
(this is motivated by upcoming changes). Added a unit test of steps
against skcms, with round-tripping in both combinations.

Change-Id: Iea3d60cd52edb5259b5576b1422ed6f856cde815
Reviewed-on: https://skia-review.googlesource.com/134660
Reviewed-by: Mike Klein <mtklein@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
6 files changed