Add SkImage::colorSpace() and SkImage::refColorSpace()

BUG=skia:

Change-Id: I31c2a2731cd70e4e5162905de0ad129516dacc6b
Reviewed-on: https://skia-review.googlesource.com/9152
Commit-Queue: Matt Sarett <msarett@google.com>
Reviewed-by: Mike Reed <reed@google.com>
2 files changed