Add SkColorSpace::isSRGB()

BUG=skia:

Change-Id: I124480a15e0c3cb01f4e22397c0a116f2d1c0d7d
Reviewed-on: https://skia-review.googlesource.com/9239
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Matt Sarett <msarett@google.com>
3 files changed