Add destination color space to shader ContextRec

BUG=skia:

Change-Id: Ib1920fffd5735ad54a5b785bbc2676ea240bdbfa
Reviewed-on: https://skia-review.googlesource.com/5611
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Brian Osman <brianosman@google.com>
6 files changed