skip gamut transform when identity

Change-Id: I3bb3ec19ee856ce4070a58a57b3bb8e8a170a5b9
Reviewed-on: https://skia-review.googlesource.com/130024
Commit-Queue: Mike Klein <mtklein@chromium.org>
Auto-Submit: Mike Klein <mtklein@chromium.org>
Reviewed-by: Brian Osman <brianosman@google.com>
3 files changed