Add support for gray + colorspace to SkCodec

In both PNG and JPEG, support passing Gray8 directly to skcms, and
remove assertions about gray never having a color xform.

Remove SkImage_Lazy hacks to strip color spaces when decoding gray.

Change-Id: I64c7b480c51a2b0c839e7eb8ed3a5fdea5aa4e41
Reviewed-on: https://skia-review.googlesource.com/150909
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
5 files changed