Remove kAsIs_CachedFormat

This was confusing and unnecessary. Added an explicit sBGR format to
handle one case. Now the CF always fully describes the color type and
transfer function (or it's legacy).

Bug: skia:
Change-Id: I8f792e8aa18cd2391aa541a9368e345d92bba828
Reviewed-on: https://skia-review.googlesource.com/11013
Reviewed-by: Matt Sarett <msarett@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
2 files changed